I have always O'd early between day 10 and 13 and have a 28 day cycle and have fallen pregnant 6 times the only time i have O'd late was after a round of PGD IVF which mucked up my cycle for a while and i O'd on day 14-16 for two months until i went back to normal so i don't think it matters your follies grow because of your hormones and my FS said it is possible to O during AF or just after but not common so don't worry i get my 1st pos and peak on OPK'S and my CBFM between day 9 and 10 and O not long after.

Good luck.