Public Class Form1
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
        Dim dt1 As Date = "01.09.2008"
        Dim dt2 As Date = "06.09.2008"
        Dim dt3 As Date = "05.09.2008"
        Dim dt4 As Date = "10.09.2008"
 
        If ZeitspannePrüfen(dt1, dt2, dt3, dt4) Then
            MsgBox("Überschneidung")
        Else
            MsgBox("Keine Überschneidung")
        End If
 
    End Sub
 
    Private Function ZeitspannePrüfen(ByVal dt1 As Date, ByVal dt2 As Date, _
                                      ByVal dt3 As Date, ByVal dt4 As Date) As _
                                      Boolean
 
        Dim t1 As Integer = dt1.DayOfYear
        Dim t2 As Integer = dt2.DayOfYear
        Dim t3 As Integer = dt3.DayOfYear
        Dim t4 As Integer = dt4.DayOfYear
 
        For N As Integer = t1 To t2
            If t3 = N Then
                Return True
                Exit Function
            End If
            If t4 = N Then
                Return True
                Exit Function
            End If
        Next
 
        For N As Integer = t3 To t4
            If t1 = N Then
                Return True
                Exit Function
            End If
            If t2 = N Then
                Return True
                Exit Function
            End If
        Next
 
        Return False
 
    End Function
End Class