Steps to reproduce:
1. Add a RadReminder component to a form
2. Set the StartNotificaton property to a TimeSpan of one hour and several minutes
3. Add a remind object to the reminder in a way that the time between now and the beginning of the appointment would be in the time interval between now and the now plus the reminder start notofication.
(e.g. this.radReminder1.StartNotification = new TimeSpan(1, 30, 0);
DateTime now = DateTime.Now;
this.radReminder1.AddRemindObject(new Appointment(now.AddMinutes(70), now.AddMinutes(90), "text"));

Start the project and show the reminder. You will see that the "Due in" time would not be correct.