diff --git a/openapi.yaml b/openapi.yaml
index c3ecc302..7a6367d1 100644
--- a/openapi.yaml
+++ b/openapi.yaml
@@ -4157,6 +4157,19 @@ paths:
                 properties:
                   enabled:
                     type: boolean
+                  auto_deactivation:
+                    type: object
+                    required: [at, timezone, label]
+                    properties:
+                      at:
+                        type: string
+                        format: date-time
+                        nullable: true
+                      timezone:
+                        type: string
+                        example: Europe/Copenhagen
+                      label:
+                        type: string
         '404':
           $ref: '#/components/responses/NotFound'
     put:
@@ -4189,6 +4202,21 @@ paths:
                 properties:
                   message:
                     type: string
+                  enabled:
+                    type: boolean
+                  auto_deactivation:
+                    type: object
+                    required: [at, timezone, label]
+                    properties:
+                      at:
+                        type: string
+                        format: date-time
+                        nullable: true
+                      timezone:
+                        type: string
+                        example: Europe/Copenhagen
+                      label:
+                        type: string
         '404':
           $ref: '#/components/responses/NotFound'
 
diff --git a/services/nginx/app/cron/Cron.php b/services/nginx/app/cron/Cron.php
index 22a18591..76c42c81 100644
--- a/services/nginx/app/cron/Cron.php
+++ b/services/nginx/app/cron/Cron.php
@@ -30,6 +30,7 @@ use goals\helpers\goals_criteria_progress_alert_frequency as Freq;
 use objects\department_lanes_o;
 use objects\department_goals_o;
 use objects\department_selfserve_tasks_o;
+use objects\department_variables_o;
 use objects\departments_o;
 use objects\bookings_o;
 use objects\logs_o;
@@ -1524,6 +1525,7 @@ function SelfserveOpeningRelayActivationCron(): array
     $candidates = selfserveOpeningCleanerRelayActivationCandidates($now);
     $summary = [
         'checked_departments' => count($candidates),
+        'disabled_departments' => 0,
         'activated_departments' => 0,
         'skipped_departments' => 0,
         'failed_departments' => 0,
@@ -1535,18 +1537,45 @@ function SelfserveOpeningRelayActivationCron(): array
     foreach ($candidates as $candidate) {
         $departmentId = (int)($candidate['department_id'] ?? 0);
         $opensAt = (string)($candidate['opens_at'] ?? '');
+        $openingDate = (string)($candidate['opening_date'] ?? $now->format('Y-m-d'));
         if ($departmentId <= 0 || $opensAt === '') {
             $summary['skipped_departments']++;
             continue;
         }
 
-        $cacheKey = selfserveOpeningCleanerRelayActivationKey($departmentId, $opensAt, $now);
-        if (selfserveOpeningCleanerRelayActivationAlreadyHandled($cacheKey)) {
-            $summary['skipped_departments']++;
+        $cacheKey = selfserveOpeningCleanerRelayActivationKey($departmentId, $opensAt, $openingDate);
+
+        try {
+            $transition = department_variables_o::withSelfServeTransitionLock(
+                $departmentId,
+                static function () use ($departmentId): array {
+                    $departmentSummary = selfserveActivateStaffedDefaultRelaysForDepartment($departmentId);
+                    if ((int)$departmentSummary['failed'] > 0) {
+                        return [
+                            'department_summary' => $departmentSummary,
+                            'department_disabled' => false,
+                        ];
+                    }
+
+                    return [
+                        'department_summary' => $departmentSummary,
+                        'department_disabled' => selfserveDisableDepartmentSelfServeForOpening($departmentId),
+                    ];
+                },
+                0
+            );
+        } catch (Throwable $throwable) {
+            $summary['failed_departments']++;
+            warn(
+                'SelfserveOpeningRelayActivationCron could not serialize transition for department '
+                . $departmentId
+                . ': '
+                . $throwable->getMessage()
+            );
             continue;
         }
 
-        $departmentSummary = selfserveActivateOpeningCleanerRelaysForDepartment($departmentId);
+        $departmentSummary = $transition['department_summary'];
         $summary['activated_relays'] += (int)$departmentSummary['activated'];
         $summary['skipped_relays'] += (int)$departmentSummary['skipped'];
         $summary['failed_relays'] += (int)$departmentSummary['failed'];
@@ -1556,6 +1585,13 @@ function SelfserveOpeningRelayActivationCron(): array
             continue;
         }
 
+        $departmentDisabled = (bool)$transition['department_disabled'];
+        if (!$departmentDisabled) {
+            $summary['failed_departments']++;
+            continue;
+        }
+
+        $summary['disabled_departments']++;
         selfserveMarkOpeningCleanerRelayActivationHandled($cacheKey);
         if ((int)$departmentSummary['activated'] > 0) {
             $summary['activated_departments']++;
@@ -1565,7 +1601,8 @@ function SelfserveOpeningRelayActivationCron(): array
     }
 
     echo "[" . date('Y-m-d H:i:s') . "][CRON] SelfserveOpeningRelayActivationCron: "
-        . $summary['activated_relays'] . " cleaner relays activated across "
+        . $summary['disabled_departments'] . " departments disabled self-serve, "
+        . $summary['activated_relays'] . " staffed-default relays activated across "
         . $summary['activated_departments'] . " departments.\n";
 
     return $summary;
@@ -1583,23 +1620,32 @@ function selfserveOpeningCleanerRelayActivationCandidates(DateTimeImmutable $now
 
     $startColumn = $weekday . '_start';
     $endColumn = $weekday . '_end';
+    $previousDate = $now->modify('-1 day');
+    $previousWeekday = strtolower($previousDate->format('l'));
+    $previousStartColumn = $previousWeekday . '_start';
+    $previousEndColumn = $previousWeekday . '_end';
     $sql = "
         SELECT
             oh.department AS department_id,
-            TIME_FORMAT(oh.`$startColumn`, '%H:%i:%s') AS opens_at,
-            TIME_FORMAT(oh.`$endColumn`, '%H:%i:%s') AS closes_at
+            TIME_FORMAT(oh.`$startColumn`, '%H:%i:%s') AS current_opens_at,
+            TIME_FORMAT(oh.`$endColumn`, '%H:%i:%s') AS current_closes_at,
+            TIME_FORMAT(oh.`$previousStartColumn`, '%H:%i:%s') AS previous_opens_at,
+            TIME_FORMAT(oh.`$previousEndColumn`, '%H:%i:%s') AS previous_closes_at
         FROM department_time_bookings_opening_hours oh
         INNER JOIN department_variables dv ON dv.department_id = oh.department
-        INNER JOIN department_lanes dl ON dl.department = oh.department
         WHERE dv.variable = 'selfserve_enabled'
           AND LOWER(TRIM(COALESCE(dv.value, ''))) IN ('true', '1', 'yes', 'on')
-          AND oh.`$startColumn` IS NOT NULL
-          AND oh.`$endColumn` IS NOT NULL
-          AND dl.deleted_at IS NULL
-          AND COALESCE(dl.selfserve_enabled, 1) = 1
-          AND dl.relay_machine_cleaner_id IS NOT NULL
-          AND TRIM(dl.relay_machine_cleaner_id) <> ''
-        GROUP BY oh.department, oh.`$startColumn`, oh.`$endColumn`
+          AND (
+            (oh.`$startColumn` IS NOT NULL AND oh.`$endColumn` IS NOT NULL)
+            OR
+            (oh.`$previousStartColumn` IS NOT NULL AND oh.`$previousEndColumn` IS NOT NULL)
+          )
+        GROUP BY
+            oh.department,
+            oh.`$startColumn`,
+            oh.`$endColumn`,
+            oh.`$previousStartColumn`,
+            oh.`$previousEndColumn`
     ";
 
     $result = $db->query($sql);
@@ -1607,14 +1653,33 @@ function selfserveOpeningCleanerRelayActivationCandidates(DateTimeImmutable $now
         return [];
     }
 
-    return array_values(array_filter(
-        $db->fetch_all($result),
-        static fn(array $row): bool => selfserveOpeningCleanerRelayWindowActive(
-            $now,
-            (string)($row['opens_at'] ?? ''),
-            (string)($row['closes_at'] ?? '')
-        )
-    ));
+    $candidates = [];
+    foreach ($db->fetch_all($result) as $row) {
+        $currentOpensAt = (string)($row['current_opens_at'] ?? '');
+        $currentClosesAt = (string)($row['current_closes_at'] ?? '');
+        if (selfserveOpeningCleanerRelayWindowActive($now, $currentOpensAt, $currentClosesAt)) {
+            $candidates[] = [
+                'department_id' => $row['department_id'] ?? null,
+                'opens_at' => $currentOpensAt,
+                'closes_at' => $currentClosesAt,
+                'opening_date' => $now->format('Y-m-d'),
+            ];
+            continue;
+        }
+
+        $previousOpensAt = (string)($row['previous_opens_at'] ?? '');
+        $previousClosesAt = (string)($row['previous_closes_at'] ?? '');
+        if (selfserveOpeningCleanerRelayOvernightCarryoverActive($now, $previousOpensAt, $previousClosesAt)) {
+            $candidates[] = [
+                'department_id' => $row['department_id'] ?? null,
+                'opens_at' => $previousOpensAt,
+                'closes_at' => $previousClosesAt,
+                'opening_date' => $previousDate->format('Y-m-d'),
+            ];
+        }
+    }
+
+    return $candidates;
 }
 
 function selfserveOpeningCleanerRelayWindowActive(
@@ -1639,6 +1704,24 @@ function selfserveOpeningCleanerRelayWindowActive(
     return $nowSeconds >= $opensAtSeconds;
 }
 
+function selfserveOpeningCleanerRelayOvernightCarryoverActive(
+    DateTimeImmutable $now,
+    ?string $opensAt,
+    ?string $closesAt
+): bool {
+    $opensAtSeconds = selfserveOpeningCleanerRelayTimeToSeconds($opensAt);
+    $closesAtSeconds = selfserveOpeningCleanerRelayTimeToSeconds($closesAt);
+    if ($opensAtSeconds === null || $closesAtSeconds === null || $opensAtSeconds <= $closesAtSeconds) {
+        return false;
+    }
+
+    $nowSeconds = ((int)$now->format('G') * 3600)
+        + ((int)$now->format('i') * 60)
+        + (int)$now->format('s');
+
+    return $nowSeconds < $closesAtSeconds;
+}
+
 function selfserveOpeningCleanerRelayTimeToSeconds(?string $time): ?int
 {
     $time = trim((string)$time);
@@ -1661,7 +1744,27 @@ function selfserveOpeningCleanerRelayTimeToSeconds(?string $time): ?int
     return ($hours * 3600) + ($minutes * 60) + $seconds;
 }
 
-function selfserveActivateOpeningCleanerRelaysForDepartment(int $departmentId): array
+function selfserveDisableDepartmentSelfServeForOpening(int $departmentId): bool
+{
+    try {
+        (new department_variables_o())
+            ->selectDepartment($departmentId)
+            ->set('selfserve_enabled', 'false');
+
+        return true;
+    } catch (Throwable $throwable) {
+        warn(
+            'SelfserveOpeningRelayActivationCron failed to disable self-serve for department '
+            . $departmentId
+            . ': '
+            . $throwable->getMessage()
+        );
+
+        return false;
+    }
+}
+
+function selfserveActivateStaffedDefaultRelaysForDepartment(int $departmentId): array
 {
     $summary = [
         'activated' => 0,
@@ -1677,17 +1780,7 @@ function selfserveActivateOpeningCleanerRelaysForDepartment(int $departmentId):
             continue;
         }
 
-        try {
-            if (!$departmentLane->isSelfServeEnabled()) {
-                $summary['skipped']++;
-                continue;
-            }
-        } catch (Throwable) {
-            $summary['skipped']++;
-            continue;
-        }
-
-        if (!selfserveLaneHasConfiguredCleanerRelay($departmentLane)) {
+        if (!selfserveLaneHasAnyConfiguredStaffedDefaultRelay($departmentLane)) {
             $summary['skipped']++;
             continue;
         }
@@ -1700,13 +1793,15 @@ function selfserveActivateOpeningCleanerRelaysForDepartment(int $departmentId):
 
         try {
             $lane = $selfserve->lane($laneId);
-            if (!selfserveLaneHasConfiguredCleanerRelay($lane->department_lane)) {
-                $summary['skipped']++;
-                continue;
-            }
-
-            $lane->setMachineCleanerRelayStatusHard(true);
-            $summary['activated']++;
+            $summary['activated'] += selfserveSetOptionalLaneRelayState($lane, 'relay_machine_program_picker_id', static function () use ($lane): void {
+                $lane->setMachineProgramPickerRelayStatusForDepartmentOperation(true);
+            });
+            $summary['activated'] += selfserveSetOptionalLaneRelayState($lane, 'relay_machine_cleaner_id', static function () use ($lane): void {
+                $lane->setMachineCleanerRelayStatusForDepartmentOperation(true);
+            });
+            $summary['activated'] += selfserveSetOptionalLaneRelayState($lane, 'relay_machine_id', static function () use ($lane): void {
+                $lane->setMachineRelayStatusForDepartmentOperation(true);
+            });
         } catch (Throwable $throwable) {
             $summary['failed']++;
             warn(
@@ -1723,19 +1818,31 @@ function selfserveActivateOpeningCleanerRelaysForDepartment(int $departmentId):
     return $summary;
 }
 
+function selfserveLaneHasAnyConfiguredStaffedDefaultRelay(?object $departmentLane): bool
+{
+    return selfserveLaneHasConfiguredRelay($departmentLane, 'relay_machine_program_picker_id')
+        || selfserveLaneHasConfiguredRelay($departmentLane, 'relay_machine_cleaner_id')
+        || selfserveLaneHasConfiguredRelay($departmentLane, 'relay_machine_id');
+}
+
 function selfserveLaneHasConfiguredCleanerRelay(?object $departmentLane): bool
+{
+    return selfserveLaneHasConfiguredRelay($departmentLane, 'relay_machine_cleaner_id');
+}
+
+function selfserveLaneHasConfiguredRelay(?object $departmentLane, string $relayProperty): bool
 {
     if (
         $departmentLane === null
-        || !isset($departmentLane->relay_machine_cleaner_id)
-        || !is_object($departmentLane->relay_machine_cleaner_id)
-        || !method_exists($departmentLane->relay_machine_cleaner_id, 'value')
+        || !isset($departmentLane->{$relayProperty})
+        || !is_object($departmentLane->{$relayProperty})
+        || !method_exists($departmentLane->{$relayProperty}, 'value')
     ) {
         return false;
     }
 
     try {
-        $relayId = trim((string)$departmentLane->relay_machine_cleaner_id->value());
+        $relayId = trim((string)$departmentLane->{$relayProperty}->value());
     } catch (Throwable) {
         return false;
     }
@@ -1743,14 +1850,35 @@ function selfserveLaneHasConfiguredCleanerRelay(?object $departmentLane): bool
     return $relayId !== '' && $relayId !== '0' && strtolower($relayId) !== 'null';
 }
 
+function selfserveSetOptionalLaneRelayState(object $lane, string $relayProperty, callable $callback): int
+{
+    if (!selfserveLaneHasConfiguredRelay($lane->department_lane ?? null, $relayProperty)) {
+        return 0;
+    }
+
+    try {
+        $callback();
+        return 1;
+    } catch (Throwable $throwable) {
+        warn(
+            'SelfserveOpeningRelayActivationCron failed to activate relay '
+            . $relayProperty
+            . ': '
+                . $throwable->getMessage()
+        );
+
+        throw $throwable;
+    }
+}
+
 function selfserveOpeningCleanerRelayActivationKey(
     int $departmentId,
     string $opensAt,
-    DateTimeImmutable $now
+    string $openingDate
 ): string {
     $normalizedOpensAt = preg_replace('/[^0-9]/', '', $opensAt) ?: 'unknown';
     return 'selfserve:opening-cleaner-relays:'
-        . $now->format('Y-m-d')
+        . $openingDate
         . ':'
         . $departmentId
         . ':'
diff --git a/services/nginx/app/modules/selfserve/cron/tasks.php b/services/nginx/app/modules/selfserve/cron/tasks.php
index 4a3f452a..9e3f2db4 100644
--- a/services/nginx/app/modules/selfserve/cron/tasks.php
+++ b/services/nginx/app/modules/selfserve/cron/tasks.php
@@ -4,8 +4,8 @@ return [
     [
         'id' => 'selfserve.activate_opening_cleaner_relays',
         'legacy_name' => 'SelfserveOpeningRelayActivationCron',
-        'name' => 'Activate self-serve opening cleaner relays',
-        'description' => 'Turns configured self-serve cleaner relays on when a department enters opening hours.',
+        'name' => 'Restore staffed relays and disable department self-serve at opening',
+        'description' => 'Restores every configured lane relay to its staffed default before disabling department self-serve when staffed opening hours begin.',
         'module' => 'selfserve',
         'handler' => 'SelfserveOpeningRelayActivationCron',
         'schedule' => ['type' => 'interval', 'seconds' => 60],
diff --git a/services/nginx/app/modules/selfserve/traits/selfserve_lane_relay_controller_t.php b/services/nginx/app/modules/selfserve/traits/selfserve_lane_relay_controller_t.php
index 792b30ab..306380c8 100644
--- a/services/nginx/app/modules/selfserve/traits/selfserve_lane_relay_controller_t.php
+++ b/services/nginx/app/modules/selfserve/traits/selfserve_lane_relay_controller_t.php
@@ -130,6 +130,11 @@ trait selfserve_lane_relay_controller_t
         return $this->setRelayStatusHard(selfserve_lane_relay::MACHINE, $on);
     }
 
+    public function setMachineRelayStatusForDepartmentOperation(bool $on): bool
+    {
+        return $this->sendRelaySwitchCommandForDepartmentOperation(selfserve_lane_relay::MACHINE, $on);
+    }
+
     /**
      * Set PROGRAM SELECTOR relay status directly, bypassing lane status guards.
      * Intended for department-level operational toggles.
@@ -161,6 +166,14 @@ trait selfserve_lane_relay_controller_t
         return $this->setRelayStatusHard(selfserve_lane_relay::MACHINE_PROGRAM_PICKER, $on);
     }
 
+    public function setMachineProgramPickerRelayStatusForDepartmentOperation(bool $on): bool
+    {
+        return $this->sendRelaySwitchCommandForDepartmentOperation(
+            selfserve_lane_relay::MACHINE_PROGRAM_PICKER,
+            $on
+        );
+    }
+
     /**
      * Set MACHINE_CLEANER relay status directly.
      * @param bool $on true to turn on, false to turn off
@@ -182,6 +195,14 @@ trait selfserve_lane_relay_controller_t
         return $this->setRelayStatusHard(selfserve_lane_relay::MACHINE_CLEANER, $on);
     }
 
+    public function setMachineCleanerRelayStatusForDepartmentOperation(bool $on): bool
+    {
+        return $this->sendRelaySwitchCommandForDepartmentOperation(
+            selfserve_lane_relay::MACHINE_CLEANER,
+            $on
+        );
+    }
+
     /**
      * Set relay status directly for a specific relay type.
      * @param selfserve_lane_relay $relay
@@ -1033,6 +1054,20 @@ trait selfserve_lane_relay_controller_t
             throw new \Exception("Cannot change relay state: Self-serve is not enabled for this lane's department.");
         }
 
+        return $this->sendRelaySwitchCommandForDepartmentOperation($relay, $on, $duration);
+    }
+
+    /**
+     * Department-level transitions deliberately bypass lane self-serve guards.
+     * Callers must serialize the transition before using this path.
+     *
+     * @throws \Exception
+     */
+    private function sendRelaySwitchCommandForDepartmentOperation(
+        selfserve_lane_relay $relay,
+        bool $on,
+        ?int $duration = null
+    ): bool {
         $relay_id = $this->getRelayId($relay);
         $payload = [
             'id' => $relay_id,
diff --git a/services/nginx/app/objects/department_time_bookings_opening_hours_o.php b/services/nginx/app/objects/department_time_bookings_opening_hours_o.php
index 43eaeea3..9231facf 100644
--- a/services/nginx/app/objects/department_time_bookings_opening_hours_o.php
+++ b/services/nginx/app/objects/department_time_bookings_opening_hours_o.php
@@ -4,6 +4,7 @@ namespace objects;
 
 use classes\db;
 use classes\object_property;
+use DateTimeImmutable;
 use Exception;
 use traits\db_object_t;
 
@@ -81,6 +82,22 @@ class department_time_bookings_opening_hours_o extends db
         }
     }
 
+    public function selectExistingByDepartment(int $department_id): bool
+    {
+        $matches = self::getFieldsWhere([
+            'department' => $department_id
+        ], [
+            'id'
+        ]);
+        if (count($matches) === 0) {
+            return false;
+        }
+
+        $this->id = $matches[0]['id'];
+        self::getObjectProperties();
+        return true;
+    }
+
     public function getObjectProperties(): void
     {
         $this->department = new object_property($this->table, $this->id, 'department', 'int', true);
@@ -197,6 +214,90 @@ class department_time_bookings_opening_hours_o extends db
         return ($startTime >= $openingStartTime && $endTime <= $openingEndTime);
     }
 
+    public function getNextOpeningStart(DateTimeImmutable $now): ?DateTimeImmutable
+    {
+        self::requireSelected();
+
+        $previousDay = $now->modify('-1 day');
+        $previousWeekdayName = self::getWeekdayName((int)$previousDay->format('N'));
+        $previousOpeningStart = $this->normalizeOpeningTime(
+            $this->{"{$previousWeekdayName}_start"}->value()
+        );
+        $previousOpeningEnd = $this->normalizeOpeningTime(
+            $this->{"{$previousWeekdayName}_end"}->value()
+        );
+        if (
+            $previousOpeningStart !== null
+            && $previousOpeningEnd !== null
+            && $previousOpeningStart > $previousOpeningEnd
+        ) {
+            $carryoverEnd = $now->setTime(
+                $previousOpeningEnd[0],
+                $previousOpeningEnd[1],
+                $previousOpeningEnd[2]
+            );
+            if ($now < $carryoverEnd) {
+                return $now;
+            }
+        }
+
+        for ($dayOffset = 0; $dayOffset <= 7; $dayOffset++) {
+            $candidateDay = $now->modify('+' . $dayOffset . ' days');
+            $weekdayName = self::getWeekdayName((int)$candidateDay->format('N'));
+            $openingStart = $this->normalizeOpeningTime($this->{"{$weekdayName}_start"}->value());
+            $openingEnd = $this->normalizeOpeningTime($this->{"{$weekdayName}_end"}->value());
+
+            if (
+                $openingStart === null
+                || $openingEnd === null
+                || $openingStart === $openingEnd
+            ) {
+                continue;
+            }
+
+            $candidateStart = $candidateDay->setTime($openingStart[0], $openingStart[1], $openingStart[2]);
+            if ($dayOffset === 0) {
+                $candidateEnd = $candidateDay->setTime($openingEnd[0], $openingEnd[1], $openingEnd[2]);
+                if ($candidateEnd <= $candidateStart) {
+                    $candidateEnd = $candidateEnd->modify('+1 day');
+                }
+
+                if ($now >= $candidateStart && $now < $candidateEnd) {
+                    return $now;
+                }
+                if ($candidateStart < $now) {
+                    continue;
+                }
+            }
+
+            return $candidateStart;
+        }
+
+        return null;
+    }
+
+    private function normalizeOpeningTime(mixed $value): ?array
+    {
+        $value = trim((string)$value);
+        if ($value === '') {
+            return null;
+        }
+
+        if (!preg_match('/^(\d{1,2}):(\d{2})(?::(\d{2}))?$/', $value, $matches)) {
+            return null;
+        }
+
+        $hours = (int)$matches[1];
+        $minutes = (int)$matches[2];
+        $seconds = isset($matches[3]) ? (int)$matches[3] : 0;
+
+        if ($hours > 23 || $minutes > 59 || $seconds > 59) {
+            return null;
+        }
+
+        return [$hours, $minutes, $seconds];
+    }
+
     /**
      * Get the name of the day of the week
      * @param int $dayOfWeek The day of the week (1 = Monday, 7 = Sunday)
@@ -216,4 +317,4 @@ class department_time_bookings_opening_hours_o extends db
             default => throw new Exception('Invalid day of the week'),
         };
     }
-}
\ No newline at end of file
+}
diff --git a/services/nginx/app/objects/department_variables_o.php b/services/nginx/app/objects/department_variables_o.php
index d64527e0..92e58ec9 100644
--- a/services/nginx/app/objects/department_variables_o.php
+++ b/services/nginx/app/objects/department_variables_o.php
@@ -59,6 +59,68 @@ class department_variables_o extends db
         }
     }
 
+    public static function withSelfServeTransitionLock(
+        int $departmentId,
+        callable $callback,
+        int $timeoutSeconds = 5
+    ): mixed {
+        if ($departmentId <= 0) {
+            throw new \InvalidArgumentException('A valid department is required for the self-serve transition lock.');
+        }
+
+        $lockName = 'selfserve:department-transition:' . $departmentId;
+        if (!self::acquireSelfServeTransitionLock($lockName, max(0, $timeoutSeconds))) {
+            throw new \RuntimeException('The department self-serve transition is already in progress.');
+        }
+
+        try {
+            return $callback();
+        } finally {
+            try {
+                self::releaseSelfServeTransitionLock($lockName);
+            } catch (\Throwable) {
+            }
+        }
+    }
+
+    private static function acquireSelfServeTransitionLock(string $lockName, int $timeoutSeconds): bool
+    {
+        global $db;
+
+        $statement = $db->prepare('SELECT GET_LOCK(?, ?) AS acquired');
+        if ($statement === false) {
+            throw new \RuntimeException('Could not prepare the department self-serve transition lock.');
+        }
+
+        try {
+            $statement->bind_param('si', $lockName, $timeoutSeconds);
+            $statement->execute();
+            $result = $statement->get_result();
+            $row = $result instanceof \mysqli_result ? $result->fetch_assoc() : null;
+
+            return (int)($row['acquired'] ?? 0) === 1;
+        } finally {
+            $statement->close();
+        }
+    }
+
+    private static function releaseSelfServeTransitionLock(string $lockName): void
+    {
+        global $db;
+
+        $statement = $db->prepare('SELECT RELEASE_LOCK(?) AS released');
+        if ($statement === false) {
+            throw new \RuntimeException('Could not prepare the department self-serve transition lock release.');
+        }
+
+        try {
+            $statement->bind_param('s', $lockName);
+            $statement->execute();
+        } finally {
+            $statement->close();
+        }
+    }
+
     /**
      * Require the department ID to be set, and throw an exception if it is not
      * @throws Exception If the department ID is not set.
@@ -198,4 +260,4 @@ class department_variables_o extends db
         return $this;
     }
 
-}
\ No newline at end of file
+}
diff --git a/services/nginx/app/openapi.yaml b/services/nginx/app/openapi.yaml
index a8ea8fe9..b622fec6 100644
--- a/services/nginx/app/openapi.yaml
+++ b/services/nginx/app/openapi.yaml
@@ -4600,6 +4600,19 @@ paths:
                 properties:
                   enabled:
                     type: boolean
+                  auto_deactivation:
+                    type: object
+                    required: [at, timezone, label]
+                    properties:
+                      at:
+                        type: string
+                        format: date-time
+                        nullable: true
+                      timezone:
+                        type: string
+                        example: Europe/Copenhagen
+                      label:
+                        type: string
         '404':
           $ref: '#/components/responses/NotFound'
     put:
@@ -4632,6 +4645,21 @@ paths:
                 properties:
                   message:
                     type: string
+                  enabled:
+                    type: boolean
+                  auto_deactivation:
+                    type: object
+                    required: [at, timezone, label]
+                    properties:
+                      at:
+                        type: string
+                        format: date-time
+                        nullable: true
+                      timezone:
+                        type: string
+                        example: Europe/Copenhagen
+                      label:
+                        type: string
         '404':
           $ref: '#/components/responses/NotFound'
 
diff --git a/services/nginx/app/routes/departmentsRoute.php b/services/nginx/app/routes/departmentsRoute.php
index e0bfcc79..890a734a 100644
--- a/services/nginx/app/routes/departmentsRoute.php
+++ b/services/nginx/app/routes/departmentsRoute.php
@@ -4,9 +4,12 @@ namespace routes;
 
 use classes\authentication;
 use classes\selfserve;
+use DateTimeImmutable;
+use DateTimeZone;
 use objects\categories_o;
 use objects\department_categories_o;
 use objects\department_lanes_o;
+use objects\department_time_bookings_opening_hours_o;
 use objects\department_variables_o;
 use objects\departments_o;
 use objects\logs_o;
@@ -330,9 +333,9 @@ class departmentsRoute
                 $enabled = $department_variables->getVariable('selfserve_enabled');
 
                 // Return the status
-                $response->success([
-                    'enabled' => $enabled === true
-                ]);
+                $response->success(
+                    $this->buildDepartmentSelfServeEnabledPayload((int)$department->id, $enabled === true)
+                );
             } else {
                 // Return an error
                 $response->error('Invalid session', 400);
@@ -368,14 +371,22 @@ class departmentsRoute
                 // Set the department variable
                 $department_variables = (new department_variables_o())->selectDepartment($department->id);
                 $enabled = self::getParameter('enabled') === 'true' || self::getParameter('enabled') === true || self::getParameter('enabled') === 1 || self::getParameter('enabled') === '1';
-                $department_variables->set('selfserve_enabled', $enabled ? 'true' : 'false');
-                $this->syncDepartmentSelfServeRelayStates((int)$department->id, $enabled);
+                department_variables_o::withSelfServeTransitionLock(
+                    (int)$department->id,
+                    function () use ($department_variables, $department, $enabled): void {
+                        $department_variables->set('selfserve_enabled', $enabled ? 'true' : 'false');
+                        $this->syncDepartmentSelfServeRelayStates((int)$department->id, $enabled);
+                    }
+                );
 
                 // Log the incident
                 (new logs_o())->add('departments', $department->id, 1, $user->id, 'EDIT_DEPARTMENT_SELFSERVE_ENABLED', 'Successfully edited department self-serve enabled status to ' . ($enabled ? 'true' : 'false'));
 
                 // Return a success message
-                $response->success(['message' => 'Department self-serve enabled status updated successfully']);
+                $response->success([
+                    'message' => 'Department self-serve enabled status updated successfully',
+                    ...$this->buildDepartmentSelfServeEnabledPayload((int)$department->id, $enabled)
+                ]);
             } else {
                 // Return an error
                 $response->error('Invalid session', 400);
@@ -593,13 +604,13 @@ class departmentsRoute
             if (!$enabled) {
                 // Self-serve disabled: restore normal/manual relay operation.
                 $this->setOptionalLaneRelayState($lane, 'relay_machine_program_picker_id', static function () use ($lane): void {
-                    $lane->setMachineProgramPickerRelayStatusHard(true);
+                    $lane->setMachineProgramPickerRelayStatusForDepartmentOperation(true);
                 });
                 $this->setOptionalLaneRelayState($lane, 'relay_machine_cleaner_id', static function () use ($lane): void {
-                    $lane->setMachineCleanerRelayStatusHard(true);
+                    $lane->setMachineCleanerRelayStatusForDepartmentOperation(true);
                 });
                 $this->setOptionalLaneRelayState($lane, 'relay_machine_id', static function () use ($lane): void {
-                    $lane->setMachineRelayStatusHard(true);
+                    $lane->setMachineRelayStatusForDepartmentOperation(true);
                 });
                 continue;
             }
@@ -643,4 +654,38 @@ class departmentsRoute
             // Best effort only; this endpoint should still update the department variable.
         }
     }
+
+    private function buildDepartmentSelfServeEnabledPayload(int $departmentId, bool $enabled): array
+    {
+        $nextDeactivationAt = $enabled
+            ? $this->getDepartmentSelfServeAutoDeactivationAt($departmentId)
+            : null;
+
+        return [
+            'enabled' => $enabled,
+            'auto_deactivation' => [
+                'at' => $nextDeactivationAt?->format(DATE_ATOM),
+                'timezone' => 'Europe/Copenhagen',
+                'label' => $nextDeactivationAt === null
+                    ? 'NEVER'
+                    : $nextDeactivationAt->format('Y-m-d H:i:s'),
+            ],
+        ];
+    }
+
+    private function getDepartmentSelfServeAutoDeactivationAt(int $departmentId): ?DateTimeImmutable
+    {
+        try {
+            $openingHours = new department_time_bookings_opening_hours_o();
+            if (!$openingHours->selectExistingByDepartment($departmentId)) {
+                return null;
+            }
+
+            return $openingHours->getNextOpeningStart(
+                new DateTimeImmutable('now', new DateTimeZone('Europe/Copenhagen'))
+            );
+        } catch (\Throwable) {
+            return null;
+        }
+    }
 }
diff --git a/services/nginx/app/tests/Unit/Selfserve/DepartmentSelfServeEnabledRelaySyncWiringTest.php b/services/nginx/app/tests/Unit/Selfserve/DepartmentSelfServeEnabledRelaySyncWiringTest.php
index 0b2fe852..04a319ab 100644
--- a/services/nginx/app/tests/Unit/Selfserve/DepartmentSelfServeEnabledRelaySyncWiringTest.php
+++ b/services/nginx/app/tests/Unit/Selfserve/DepartmentSelfServeEnabledRelaySyncWiringTest.php
@@ -6,16 +6,28 @@ it('syncs lane relay states when department self-serve enabled flag changes', fu
     expect($routeContent)->not->toBeFalse();
     expect($routeContent)->toContain('/departments/self-serve/enabled');
     expect($routeContent)->toContain('$this->syncDepartmentSelfServeRelayStates((int)$department->id, $enabled);');
+    expect($routeContent)->toContain('department_variables_o::withSelfServeTransitionLock');
     expect($routeContent)->toContain('if (!$enabled) {');
     expect($routeContent)->toContain('// Self-serve disabled: restore normal/manual relay operation.');
-    expect($routeContent)->toContain('setMachineProgramPickerRelayStatusHard(true)');
-    expect($routeContent)->toContain('setMachineRelayStatusHard(true)');
+    expect($routeContent)->toContain('setMachineProgramPickerRelayStatusForDepartmentOperation(true)');
+    expect($routeContent)->toContain('setMachineRelayStatusForDepartmentOperation(true)');
     expect($routeContent)->toContain('!$department_lane->isSelfServeEnabled()');
     expect($routeContent)->toContain('setMachineProgramPickerRelayStatus(false)');
-    expect($routeContent)->toContain('setMachineCleanerRelayStatusHard(true)');
+    expect($routeContent)->toContain('setMachineCleanerRelayStatusForDepartmentOperation(true)');
     expect($routeContent)->toContain('setMachineRelayStatus(false)');
     expect($routeContent)->not->toContain('setMachineProgramPickerRelayStatusHard(false)');
     expect($routeContent)->not->toContain('setMachineCleanerRelayStatusHard(false)');
     expect($routeContent)->not->toContain('setMachineRelayStatusHard(false)');
     expect($routeContent)->not->toContain('setMachineCleanerRelayStatus(false)');
 });
+
+it('uses the supported prepared database API for the department transition lock', function (): void {
+    $variableObject = file_get_contents(app_path('objects/department_variables_o.php'));
+
+    expect($variableObject)->not->toBeFalse()
+        ->and($variableObject)->not->toContain('$database->selectOne')
+        ->and($variableObject)->toContain("\$db->prepare('SELECT GET_LOCK(?, ?) AS acquired')")
+        ->and($variableObject)->toContain("\$statement->bind_param('si', \$lockName, \$timeoutSeconds)")
+        ->and($variableObject)->toContain("\$db->prepare('SELECT RELEASE_LOCK(?) AS released')")
+        ->and($variableObject)->toContain("\$statement->bind_param('s', \$lockName)");
+});
diff --git a/services/nginx/app/tests/Unit/Selfserve/SelfserveOpeningRelayActivationCronTest.php b/services/nginx/app/tests/Unit/Selfserve/SelfserveOpeningRelayActivationCronTest.php
index 5a6fc362..bf54e281 100644
--- a/services/nginx/app/tests/Unit/Selfserve/SelfserveOpeningRelayActivationCronTest.php
+++ b/services/nginx/app/tests/Unit/Selfserve/SelfserveOpeningRelayActivationCronTest.php
@@ -7,10 +7,12 @@ it('registers an opening-time self-serve cleaner relay activation cron', functio
     expect($tasks[0]['id'])->toBe('selfserve.activate_opening_cleaner_relays');
     expect($tasks[0]['legacy_name'])->toBe('SelfserveOpeningRelayActivationCron');
     expect($tasks[0]['handler'])->toBe('SelfserveOpeningRelayActivationCron');
+    expect($tasks[0]['name'])->toContain('disable department self-serve');
+    expect($tasks[0]['description'])->toContain('every configured lane relay');
     expect($tasks[0]['schedule'])->toBe(['type' => 'interval', 'seconds' => 60]);
 });
 
-it('activates only configured cleaner relays after department opening time', function (): void {
+it('disables department self-serve and restores staffed relay defaults after department opening time', function (): void {
     $cronContent = file_get_contents(app_path('cron/Cron.php'));
 
     expect($cronContent)->not->toBeFalse();
@@ -18,11 +20,41 @@ it('activates only configured cleaner relays after department opening time', fun
     expect($cronContent)->toContain("new DateTimeZone('Europe/Copenhagen')");
     expect($cronContent)->toContain('department_time_bookings_opening_hours');
     expect($cronContent)->toContain("dv.variable = 'selfserve_enabled'");
-    expect($cronContent)->toContain('dl.selfserve_enabled');
-    expect($cronContent)->toContain('relay_machine_cleaner_id');
+    expect($cronContent)->toContain("->set('selfserve_enabled', 'false')");
+    expect($cronContent)->toContain('use objects\department_variables_o;');
+    expect($cronContent)->toContain('selfserveActivateStaffedDefaultRelaysForDepartment');
     expect($cronContent)->toContain('$nowSeconds >= $opensAtSeconds && $nowSeconds < $closesAtSeconds');
-    expect($cronContent)->toContain('setMachineCleanerRelayStatusHard(true)');
+    expect($cronContent)->toContain('selfserveOpeningCleanerRelayOvernightCarryoverActive');
+    expect($cronContent)->toContain('$previousDate = $now->modify(\'-1 day\')');
+    expect($cronContent)->not->toContain('if (selfserveOpeningCleanerRelayActivationAlreadyHandled($cacheKey))');
+    expect($cronContent)->not->toContain('if (!$departmentLane->isSelfServeEnabled())');
+    expect($cronContent)->toContain('throw $throwable;');
+    expect($cronContent)->toContain('department_variables_o::withSelfServeTransitionLock');
+    expect(strpos($cronContent, 'selfserveActivateStaffedDefaultRelaysForDepartment($departmentId)'))
+        ->toBeLessThan(strpos($cronContent, 'selfserveDisableDepartmentSelfServeForOpening($departmentId)'));
+    expect($cronContent)->toContain('setMachineProgramPickerRelayStatusForDepartmentOperation(true)');
+    expect($cronContent)->toContain('setMachineCleanerRelayStatusForDepartmentOperation(true)');
+    expect($cronContent)->toContain('setMachineRelayStatusForDepartmentOperation(true)');
     expect($cronContent)->toContain('selfserve:opening-cleaner-relays:');
-    expect($cronContent)->not->toContain('setMachineRelayStatusHard(true)');
-    expect($cronContent)->not->toContain('setMachineProgramPickerRelayStatusHard(true)');
+});
+
+it('exposes next self-serve auto deactivation metadata from the department endpoint', function (): void {
+    $routeContent = file_get_contents(app_path('routes/departmentsRoute.php'));
+    $openingHoursContent = file_get_contents(app_path('objects/department_time_bookings_opening_hours_o.php'));
+
+    expect($routeContent)->not->toBeFalse();
+    expect($openingHoursContent)->not->toBeFalse();
+    expect($routeContent)->toContain('buildDepartmentSelfServeEnabledPayload');
+    expect($routeContent)->toContain('selectExistingByDepartment($departmentId)');
+    expect($routeContent)->toContain("'auto_deactivation'");
+    expect($routeContent)->toContain("'label' => \$nextDeactivationAt === null");
+    expect($routeContent)->toContain("'NEVER'");
+    expect($openingHoursContent)->toContain('function getNextOpeningStart(DateTimeImmutable $now): ?DateTimeImmutable');
+    expect($openingHoursContent)->toContain('$openingStart === null');
+    expect($openingHoursContent)->toContain('$openingEnd === null');
+    expect($openingHoursContent)->toContain('$openingStart === $openingEnd');
+    expect($openingHoursContent)->toContain('$dayOffset <= 7');
+    expect($openingHoursContent)->toContain('$previousWeekdayName');
+    expect($openingHoursContent)->toContain('return $now;');
+    expect(file_get_contents(app_path('openapi.yaml')))->toContain('auto_deactivation:');
 });