Private Sub Worksheet_Change(ByVal Target As Range)
    Dim cell                  As Range
    On Error GoTo oops
    If Not Intersect(Target, Range("B3:AS38")) Is Nothing Then
        Application.EnableEvents = False
        For Each cell In Intersect(Target, Range("B3:AS38")).Cells
            Cells(cell.Row, "AT").Value = Date
        Next cell
    End If
oops:
    Application.EnableEvents = True
End Sub