Private Function GetTimeIntervall(Byval abZeit As Date, Byval bisZeit As Date) _
  As String
     Dim n As Variant
     Dim h As String, m As String
 
     ' Zeit in kleinstes Intervall zerlegen
     n = DateDiff("s",abZeit, bisZeit)
 
     h = Format((n  3600),"00")
     n = n MOD 3600
     m = Format((n  60), "00")
     n = Format((n MOD 60), "00")
 
     GetTimeIntervall = h & ":" & m & ":" & n
End Function