Option Explicit
Dim StartTime As Date
Dim StopTime As Date
Private Sub sevVon_Change()
  Change
End Sub
 
Private Sub sevBis_Change()
  Change
End Sub
Private Function Change() As Boolean
  StartTime = sevVon.Value
  StopTime = sevBis.Value
  'Ist die eingegebene Zeit plausibel?
  If StartTime >= StopTime Then
    sevVon.ForeColor = vbRed
    sevBis.ForeColor = vbRed
    Change = False
  Else
    sevVon.ForeColor = vbBlack
    sevBis.ForeColor = vbBlack
  End If
End Function