It really depends on your body and how well it adjusts to working on its own natural hormones- rather than being dictated by a pill.

For some women, ovulation happens right after getting off and for others it can take months.

I would suggest you try charting for at least the next three cycles- this will help you to see what is normal for you and give you a much better idea of when your fertile window is.  Taking Charge of Your Fertility by Toni Weschler is a great book and I would definitly reccomend reading. There are also many sites that offer free basic charting.