It's as the anon above me says: once the deadline passes, the countdown starts counting up instead of down. It's displaying how long it's been since the deadline, not how long is left to it - when you looked, it was showing three hours past the deadline, not three hours to it.

No one was defaulted early. There was actually about a five minute grace period following the deadline before I defaulted incomplete assignments, in case anyone was in the process of posting right at that moment.