Sub Test()
Dim Cel As Range, S As String
Set Cel = Selection(1, 1).MergeArea(1, 1)
S = Cel.Value
If S Like "####-####/####-####" Then
Cel.Formula = "=""" & Mid$(S, 6, 2) & ":" & Mid$(S, 8, 2) & """-""" & Mid$(S, 1, 2) & ":" & Mid$(S, 3, 2) _
& """+""" & Mid$(S, 16, 2) & ":" & Mid$(S, 18, 2) & """-""" & Mid$(S, 11, 2) & ":" & Mid$(S, 13, 2) & """"
Cel.NumberFormat = "[h]:mm": End If
End Sub