Fix station events that use update loops (#15834)

Content.Server/StationEvents/Components/StationEventComponent.cs

@@ -52,7 +52,7 @@ public sealed class StationEventComponent : Component
     ///     How long the event lasts.
     /// </summary>
     [DataField("duration")]
-    public TimeSpan Duration = TimeSpan.FromSeconds(1);
+    public TimeSpan? Duration = TimeSpan.FromSeconds(1);
 
     /// <summary>
     ///     The max amount of time the event lasts.
@@ -85,5 +85,5 @@ public sealed class StationEventComponent : Component
     /// When the station event starts.
     /// </summary>
     [DataField("endTime", customTypeSerializer: typeof(TimeOffsetSerializer))]
-    public TimeSpan EndTime;
+    public TimeSpan? EndTime;
 }