It all depends. You can never tell.
I've take provera many times before (as well as prometrium) and it has effected my differently everytime.
This last time (just this month) I was rxed a 14 day cycle (horrid) and actually started af on day 12. So you just never know. In the past though it is normally 2-3 days after my last pill. Unless it doesn't start at all....
Good luck. I hope the side effects have been minimal!