Private Function GetHours(ByVal date1 As Date, ByVal date2 As Date, _
      Optional ByVal tarifAb As Integer = 6, Optional ByVal tarifBis As Integer _
      = 22) As Double()
        Dim tarife(1) As Double
        Dim nextPointDate As Date
        Dim hochTarif As Boolean
        tarife(0) = 0
        tarife(1) = 0
 
        If date1.Hour < tarifAb Then
            nextPointDate = date1.AddMinutes((date1.Hour * 60 + date1.Minute) * _
              (-1)).AddHours(tarifAb)
            tarife(1) += nextPointDate.Subtract(date1).Minutes + _
            nextPointDate.Subtract(date1).Hours * 60
            hochTarif = True
        Else
            nextPointDate = date1.AddMinutes((date1.Hour * 60 + date1.Minute) * _
              (-1)).AddHours(tarifBis)
            tarife(0) += nextPointDate.Subtract(date1).Minutes + _
            nextPointDate.Subtract(date1).Hours * 60
            hochTarif = False
        End If
 
        Dim hochtarifH As Integer
        If tarifAb < tarifBis Then
            hochtarifH = tarifBis - tarifAb
        Else
            hochtarifH = (24 - tarifAb) + tarifBis
        End If
        Dim niedertarifH As Integer = 24 - hochtarifH
 
 
        Do
            Dim actualDate As Date = nextPointDate
            If hochTarif Then
                nextPointDate = nextPointDate.AddHours(hochtarifH)
                If nextPointDate.Subtract(actualDate) < date2.Subtract( _
                  actualDate) Then
                    tarife(0) += hochtarifH * 60
                Else
                    nextPointDate = actualDate
                    Exit Do
                End If
            Else
                nextPointDate = nextPointDate.AddHours(niedertarifH)
                If nextPointDate.Subtract(actualDate) < date2.Subtract( _
                  actualDate) Then
                    tarife(1) += niedertarifH * 60
                Else
                    nextPointDate = actualDate
                    Exit Do
                End If
            End If
 
            hochTarif = Not hochTarif
        Loop
 
        Dim rest As Integer = date2.Subtract(nextPointDate).Minutes + _
          date2.Subtract(nextPointDate).Hours * 60
        If hochTarif Then
            tarife(0) += rest
        Else
            tarife(1) += rest
        End If
        tarife(0) = tarife(0) / 60
        tarife(1) = tarife(1) / 60
 
        Return tarife
    End Function

Dim s() As Double = GetHours(CDate(TextBox1.Text), CDate(TextBox2.Text))
Label1.Text = s(0) & "Stunden Hochtarif" & vbCrLf & s(1) & "Stunden Niedertarif"