Private Sub Worksheet_Change(ByVal Target As Range)
If flag = True Then Exit Sub
If Target.Count > 1 Then Exit Sub
If Not Intersect(Target, Range("a1:b24")) Is Nothing Then
flag = True
Select Case Len(Target.Value)
Case 1
Target.Value = "00:0" & Target.Value
Case 2
Target.Value = "00:" & Target.Value
Case 3
Target.Value = "0" & Mid(Target.Value, 1, 1) & ":" & Mid(Target.Value, 2)
Case 4
Target.Value = Mid(Target.Value, 1, 2) & ":" & Mid(Target.Value, 3)
End Select
End If
flag = False
End Sub