A small point to go along with Crowley ambush. Obama must have been getting signals from someone in the audience when Romney’s time limit was over or close to the limit to interrupt him. I doubt Obama had a stop watch in his head.
There was a big countdown timer there. You could occasionally see it during the debate.
IMHO, those numbers should be displayed continually at the top of the TV screen (plus running totals per candidate) so everyone can see how the time is really being allocated.