You can do this at form level.
Place a txtbox on the form (it can be hidden if desired), set the Control Source for the txtbox to a Date/Time field in the table to store the info. Use the form's Before Update event to populate the txtbox.
Private Sub Form_BeforeUpdate(Cancel As Integer)
Me.YourTxtBoxName = Now()
End Sub
(change "YourTxtBoxName" to the name of the added txtbox)
The On Before Update event of the form will only fire if it is a new record or if the existing record has been altered.
HTH
RDH Ricky Hicks
Birmingham, Alabama