I tried it your suggestion but it does not work. Is there other solution?

I need this because we want to display the start time and duration on the Appoinment subject. 

private void dayView_AfterAppointmentsMoved(object sender, AfterAppointmentsMovedEventArgs e)
{
    UltraDayView dayView = sender as UltraDayView;
    UltraCalendarInfo calendarInfo = dayView.CalendarInfo;
    SelectedAppointmentsCollection selectedAppointments = calendarInfo.SelectedAppointments;

    for ( int i = 0; i < selectedAppointments.Count; i ++ )
    {
        Appointment appointment = selectedAppointments[i];
        appointment.Subject = appointment.StartDateTime.ToShortTimeString();
    }
}