Private Sub Worksheet_SelectionChange(ByVal Target As Range)
If Target.Count > 1 Then Exit Sub
If Not Intersect(Target, Range("C1:C1000")) Is Nothing Then
If Cells(Target.Row, "A") <> "" Then
Target = Now
Cells(Target.Row, "D") = Now - Cells(Target.Row, "B")
End If
End If
End Sub