You would have to create a macro, the easiest form of macro for this
would be an event macro. You could trigger it on replacing an empty
cell in a specific column, or when another column is filled in.
DateTimeStamp in Column A, on first entry in any other column on row (#datetimestamp)
http://www.mvps.org/dmcritchie/excel/event.htm#datetimestamp
Place current date constant in Column A when Column B changes (#autodate)
http://www.mvps.org/dmcritchie/excel/event.htm#autodate
The following will put the time into Column B when an entry is made in Column A
install by right click on sheet tab, View code, .place the following code there
Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Column <> 1Then Exit Sub
If Target.Row = 1 Then Exit Sub
If IsEmpty(Target.Offset(0, 1)) Then
Target.Offset(0, 1) = Time
Target.offset(0, 1).numberformat = "hh:mm:ss.00"
End If
End Sub