Hi Michael J.,
To override this behavior, please handle AppointmentUpdate
|protected void RadScheduler1_AppointmentUpdate(object sender, AppointmentUpdateEventArgs e)
| if(e.Appointment.Duration.TotalHours >= 24)
| e.ModifiedAppointment.End = e.ModifiedAppointment.Start.AddHours(0.5);
This code checks if the appointment is all day and if it is, makes its duration half an hour when dragged to an hour row.
Please, let us know if you continue to experience problems with this case.
the Telerik team