changed from dateTime to duration

lib/model/alarm/relative_time_alarm.dart

@@ -4,7 +4,7 @@ class RelativeTimeAlarm implements Alarm {
   @override
   final String id;
 
-  final DateTime triggerAt;
+  final Duration triggerAt;
 
   @override
   final AlarmType alarmType;
@@ -15,7 +15,7 @@ class RelativeTimeAlarm implements Alarm {
   factory RelativeTimeAlarm.fromJson(Map<String, dynamic> json) {
     return RelativeTimeAlarm(
       id: json['id'] as String,
-      triggerAt: DateTime.parse(json['triggerAt'] as String),
+      triggerAt: Duration(minutes: int.tryParse(json['triggerAt']) ?? 0),
     );
   }
 
@@ -23,7 +23,7 @@ class RelativeTimeAlarm implements Alarm {
   Map<String, dynamic> toJson() {
     return {
       'id': id,
-      'triggerAt': triggerAt.toIso8601String(),
+      'triggerAtMinutes': triggerAt.inMinutes,
       'alarmType': alarmType.toJson(),
     };
   }

lib/model/requests/create_relative_time_alarm_request.dart

@@ -3,7 +3,7 @@ import '../alarm/relative_time_alarm.dart';
 import 'create_alarm_request.dart';
 
 class CreateRelativeTimeAlarmRequest extends CreateAlarmRequest {
-  final DateTime? triggerAt;
+  final Duration? triggerAt;
 
   const CreateRelativeTimeAlarmRequest({this.triggerAt})
     : super(alarmType: AlarmType.timeRelative);