Ich schätze mal du willst die Zeit bestimmen die dazwischen liegt ...

Option Explicit

Sub blablub()
  
  Dim dtVon(1 To 2) As Date
  Dim dtBis(1 To 2) As Date
  
  dtVon(1) = "00:30:00": dtVon(2) = "23:30:00"
  dtBis(1) = "23:30:00": dtBis(2) = "00:30:00"
  
  Dim tmp As String
  Dim i As Long
  
  For i = 1 To 2
    tmp = tmp & IIf(tmp <> "", vbNewLine & vbNewLine, "") & _
            dtVon(i) & " - " & dtBis(i) & " = " & IrgendEinGerassel(dtVon(i), dtBis(i))
  Next
  
  MsgBox tmp
  
End Sub

Function IrgendEinGerassel(ZeitVon As Date, ZeitBis As Date) As Date
  
  Dim t1 As Date
  Dim t2 As Date
  
  t1 = DateAdd("d", 1, Format$(ZeitVon, "dd.mm.yyyy")) & " " & TimeValue(ZeitVon)
  t2 = DateAdd("d", 1 + Abs(ZeitVon > ZeitBis), Format$(ZeitBis, "dd.mm.yyyy")) & " " & TimeValue(ZeitBis)
  
  IrgendEinGerassel = t1 - t2
  
End Function