right click on sheet tab>view code>insert this>save workbook
your time must be entered with FOUR digits: 0525, 1450, etc
Private Sub Worksheet_Change(ByVal Target As Excel.Range)
If Target.Column = 4 Then
On Error GoTo endit
Application.EnableEvents = False
Target = Left(Target, 2) & ":" & Right(Target, 2)
End If
endit:
Application.EnableEvents = True
End Sub