Time/Date Function

you can also try this, this will help you to add the start time and end time.

This will add the start time in column A and end time in column B, if the user clicks the button.

Sub r()
rr = Application.WorksheetFunction.CountA(Columns(1))

Range("A1").Select
Range("A" & rr).Select
If ActiveCell.Offset(0, 1).Value <> "" Then
Selection.Offset(1, 0).Select
ActiveCell.Value = Format(Now(), "HH:MM:SS")
Else
Selection.Offset(0, 1).Select
ActiveCell.Value = Format(Now(), "HH:MM:SS")
End If

End Sub