diff --git a/src/model/schedule.ts b/src/model/schedule.ts
index 8bd231b..e60241b 100644
--- a/src/model/schedule.ts
+++ b/src/model/schedule.ts
@@ -134,8 +134,8 @@ export class ScheduleModel {
 
 					const doctor = exception?.override_doctor ?? series.doctor;
 					const room = exception?.override_room ?? series.room;
-					const eventStart = exception?.override_start_at ? new Date(exception.override_start_at) : defaultStart;
-					const eventEnd = exception?.override_end_at ? new Date(exception.override_end_at) : defaultEnd;
+					const eventStart = exception?.override_start_at ? exception.override_start_at : defaultStart;
+					const eventEnd = exception?.override_end_at ? exception.override_end_at : defaultEnd;
 					const eventTitle = exception?.override_title || series.title;
 
 					const roomId = room?.id || null;
@@ -151,8 +151,8 @@ export class ScheduleModel {
 						room_name: roomName,
 						doctor_id: doctorId,
 						doctor_name: doctorName,
-						start_at: eventStart.toISOString(),
-						end_at: eventEnd.toISOString(),
+						start_at: eventStart,
+						end_at: eventEnd,
 						quota: series.quota ?? null,
 						used_quota: usageMap.get(`${series.id}:${occurrenceYmd}`) || 0,
 						left_quota:
@@ -462,8 +462,8 @@ export class ScheduleModel {
 		};
 	}
 
-	private static combineDateAndTime(ymd: string, hhmmss: string): Date {
-		return new Date(`${ymd}T${hhmmss}`);
+	private static combineDateAndTime(ymd: string, hhmmss: string) {
+		return `${ymd} ${hhmmss}`;
 	}
 
 	private static startOfDay(date: Date): Date {