Sorry, I should have made myself clear..
I am talking about the clock that starts ticking when you are officially out of status. If the student just leaves the US, then he or she would not have accumulated and out-of-status duration technically. In this case, he is no doubt out of status, but due to the stamp D/S unless he gets caught or see a judge, he wont be tagged as being out of status. This might help him to come back in the near future when his wife becomes a Citizen or his priority date is current. However, what I am not sure and an atty might be needed for is, if he sees a judge and he tags him as being out of status, does the time start right after that or is the clock set retroactively to when he stopped attending school.......