Not sure of your set-up. Assuming you are talking about data entry on the
bound Form, it sounds like you can use the CheckBox_AfterUpdate Event to set
the value of a TextBox (bound to the Date Field). When the Form updates the
data into the Table, the (today) date value will be updated also. The code
should be something like:
Private Sub CheckBox_AfterUpdate()
Me.txtDateChecked = Date()
End Sub