Use ini timezone setting

config/config.default.php

@@ -115,7 +115,7 @@ return [
     'max_freeloadable_shifts' => 2,
 
     // Local timezone
-    'timezone'                => env('TIMEZONE', 'Europe/Berlin'),
+    'timezone'                => env('TIMEZONE', ini_get('date.timezone') ?: 'Europe/Berlin'),
 
     // Multiply 'night shifts' and freeloaded shifts (start or end between 2 and 6 exclusive) by 2
     'night_shifts'            => [

includes/application.php

@@ -24,7 +24,8 @@ $app->bootstrap($appConfig);
 /**
  * Configure application
  */
-date_default_timezone_set($app->get('config')->get('timezone'));
+$timezone = $app->get('config')->get('timezone');
+ini_set('date.timezone', $timezone);
 
 if (config('environment') == 'development') {
     $errorHandler = $app->get('error.handler');