With your form open in design view, right click on the control you wish to use as the first field. Select Properties, Select the Event Tab. Select After Update. Click on the ellipsis (...). Select the Code option. Paste in the code I gave you changing the control names to correspond to yours. You will also need to change the name of the after update command to agree with your control name. Post back if you have any issues.
Code:
Private Sub FName_AfterUpdate()
Me.Tdate.Value = Date
Me.Dtime.Value = Time()
End Sub
Alan