public virtual List<IEvent> GetAppointmentsInInterval(DateTimeInterval interval)
        {
            List<IEvent> currentEvents = new List<IEvent>();
            IList<IEvent> appointments = this.Appointments;
            int appointmentCount = appointments.Count;
            for (int i = 0; i < appointmentCount; i++)
            {
                IEvent currentAppointment = appointments[i];

                DateTimeInterval appointmentInterval = this.GetEventInterval(currentAppointment);
                if (interval.IntersectsWith(appointmentInterval))
                {
                    currentEvents.Add(currentAppointment);
                }
            }

            return currentEvents;
        }

        private DateTimeInterval GetEventInterval(IEvent evt)
        {
            return new DateTimeInterval(evt.Start, evt.End);
        }

 Dim myStartDate As DateTime
 Sub New()
      
     InitializeComponent()

     Me.RadScheduler1.ActiveViewType = SchedulerViewType.MultiDay

     Dim multiDayView As New SchedulerMultiDayView()
     Dim startDate As Date = Date.Today
     multiDayView.Intervals.Add(startDate, 2)
     multiDayView.Intervals.Add(startDate.AddDays(4), 3)
     Me.RadScheduler1.ActiveView = multiDayView

     myStartDate = DateTime.Today.AddHours(10).AddMinutes(30)
     Dim appointment As New Appointment(myStartDate, myStartDate.AddHours(1), "Test")
     appointment.AllDay = True
     Me.RadScheduler1.Appointments.Add(appointment)

 End Sub

 Private Sub RadButton1_Click(sender As Object, e As EventArgs) Handles RadButton1.Click
     Dim multiDayView As SchedulerMultiDayView = TryCast(Me.RadScheduler1.ActiveView, SchedulerMultiDayView)

     Dim endDate As DateTime = myStartDate.AddMinutes(1)
     Dim interval As DateTimeInterval = New DateTimeInterval(myStartDate, endDate)
     Dim appointments = multiDayView.GetAppointmentsInInterval(interval)
 End Sub

Private Sub RadButton1_Click(sender As Object, e As EventArgs) Handles RadButton1.Click
    Dim multiDayView As SchedulerMultiDayView = TryCast(Me.RadScheduler1.ActiveView, SchedulerMultiDayView)

    Dim endDate As DateTime = myStartDate.AddMinutes(1)
    Dim interval As DateTimeInterval = New DateTimeInterval(myStartDate, endDate)
    Dim appointments = GetAppointmentsInInterval(interval)
End Sub

Public Overridable Function GetAppointmentsInInterval(ByVal interval As DateTimeInterval) As List(Of IEvent)
    Dim currentEvents As List(Of IEvent) = New List(Of IEvent)()
    Dim appointments As IList(Of IEvent) = Me.RadScheduler1.Appointments
    Dim appointmentCount As Integer = appointments.Count

    For i As Integer = 0 To appointmentCount - 1
        Dim currentAppointment As IEvent = appointments(i)
        Dim appointmentInterval As DateTimeInterval = Me.GetEventInterval(currentAppointment)

        If interval.IntersectsWith(appointmentInterval) Then
            currentEvents.Add(currentAppointment)
        End If
    Next

    Return currentEvents
End Function

Private Function GetEventInterval(ByVal evt As IEvent) As DateTimeInterval
    If evt.AllDay Then
        Return New DateTimeInterval(evt.Start, evt.Start.AddHours(24).AddSeconds(-1))
    End If

    Return New DateTimeInterval(evt.Start, evt.[End])
End Function