Is it possible that ovulation time alters due to stopping the pill?

It's unusual to have your period on the same numerical date of the month when you're on Birth Control pills. Since the pill goes on a cycle of 28 days, and a month has anywhere from 28 to 21 days, you'd normally have your period every 28 days, which means if you had it on the 21st of July, you'd expect it on the 18th of August, the 15th of september, the 13th of October, the 10th of November. There is no reason to expect your period to follow the calendar on or off the pill, since neither your ovaries nor the pill know that "Thirty days hath September..." etc.