Submit your dissertation by the deadline. You are required to submit your dissertation on or before the deadline in order to complete your degree for the given term.
This is a strict rule. You must click submit by midnight of the deadline. The policy is that if you click submit even one minute late, you graduate the next semester. If it is the end of the window period, you will be expected to enroll for the next semester.
The ProQuest website records the time of every action you make.