Private Sub Zeitdifferenz(ByVal StartZeit As Date, ByVal EndZeit As Date, _
                          ByRef Periode1 As Integer, ByRef Periode2 As Integer)
 
        Dim p1s As Integer = 421    '07:01
        Dim p1e As Integer = 1380  '23:00
        Dim zeit As Date = StartZeit, tm As Integer
 
        Periode1 = 0 : Periode2 = 0
 
        While zeit < EndZeit
            tm = zeit.Hour * 60 + zeit.Minute
            If tm >= p1s And tm <= p1e Then
                Periode1 += 1
            Else
                Periode2 += 1
            End If
            zeit = zeit.AddMinutes(1)
        End While
    End Sub