Figured this out:
oApp =
New Telerik.Web.UI.Appointment
oApp.Description = GetEntityTypeName(oTemp.Type)
oApp.Subject = oTemp.Name
oApp.Start = RadScheduler1.DisplayToUtc(oTemp.StartTime)
oApp.End = RadScheduler1.DisplayToUtc(oTemp.EndTime)
oApp.ID = oTemp.ID
RadScheduler1.InsertAppointment(oApp)
The reason this did not work for me at first, was that my dates only contained a time of day and not a date.