fixes

src/server/HSMServer.Core/AlertSchedule/AlertScheduleParser.cs

@@ -338,13 +338,13 @@ public object ReadYaml(IParser parser, Type type, ObjectDeserializer rootDeseria
         public void WriteYaml(IEmitter emitter, object value, Type type)
         {
             var timeSpan = (TimeSpan)value;
-            emitter.Emit(new Scalar(timeSpan.ToString(@"hh\:mm")));
+            emitter.Emit(new Scalar(timeSpan.ToString(@"HH\:mm")));
         }
 
         public void WriteYaml(IEmitter emitter, object value, Type type, ObjectSerializer serializer)
         {
             var timeSpan = (TimeSpan)value;
-            emitter.Emit(new Scalar(timeSpan.ToString(@"hh\:mm")));
+            emitter.Emit(new Scalar(timeSpan.ToString(@"HH\:mm")));
         }
     }
 

src/server/HSMServer.Core/AlertSchedule/AlertScheduleProvider.cs

@@ -9,7 +9,7 @@
 
 namespace HSMServer.Core.Schedule
 {
-    public class AlertScheduleProvider : IAlertScheduleProvider
+    public class AlertScheduleProvider : IAlertScheduleProvider, IDisposable
     {
         private readonly TimeSpan CLEANUP_PERIOD = TimeSpan.FromMinutes(5);
 
@@ -189,7 +189,7 @@ public void CleanupIntervalCache()
             {
                 lock (_lock)
                 {
-                    var cleanupThreshold = DateTime.UtcNow.AddMinutes(1);
+                    var cleanupThreshold = DateTime.UtcNow.AddMinutes(-1);
                     int totalRemoved = 0;
 
                     foreach (var cacheEntry in _cache.Values)

src/server/HSMServer.Core/Cache/TreeValuesCache.cs

@@ -2298,7 +2298,7 @@ public List<BaseSensorModel> GetSensorsByAlertSchedule(Guid id)
 
             foreach (var sensor in _sensorsById.Values)
             {
-                if (sensor.Policies.TimeToLive.ScheduleId == id)
+                if (sensor.Policies.TimeToLive?.ScheduleId == id)
                 {
                     result.Add(sensor);
                     continue;