To reproduce:

public Form1()
{
    InitializeComponent();
    this.radScheduler1.ActiveViewType = SchedulerViewType.Month;
    
    Appointment appointment = new Appointment(DateTime.Today.AddHours(23).AddMinutes(45), new TimeSpan(0,15,0), "Meeting");
    DailyRecurrenceRule rrule = new DailyRecurrenceRule(appointment.Start, 1, 10); 
    appointment.RecurrenceRule = rrule;
    this.radScheduler1.Appointments.Add(appointment);
    this.radScheduler1.EnableExactTimeRendering = true;
    
}

Click "This month" in RadSchedulerNavigator.

Workaround: In order to deal with the border case with appointment ending at 00:00h, use a new TimeSpan(0,14,59)