I'm not sure this is what you really want but this is what I think you want. You already had macros that I modified to automatically place a time at the last cell in the row of either Start or End time.
Private Sub CommandButton1_Click()
Cells(Rows.Count, 6).End(xlUp).Offset(1, 0) = Time
End Sub

Private Sub CommandButton2_Click()
Cells(Rows.Count, 7).End(xlUp).Offset(1, 0) = Time
End Sub
Hope this help