Your body's version of "normal" cycling may resume immediately or a year or more later. There are many factors that contribute to how quickly your body settles back into its own routine.
My experience: I always had 35ish-day cycles before BC. The BC I used forces a 28-day rotation of hormones. It took an entire year of cycles ranging from 23 days to 66 days long before I finally settled back into my old 35 day norm.
If you are wanting to continue to avoid pregnancy, you must consider yourself "at risk" as soon as you stop taking your BC. You must be ready immediately with alternate methods of contraception.
If you are wanting to achieve pregnancy, though, realize that you could have quite a wait before your fertility stabilizes. Some are lucky and get pregnant immediately after quitting BC, but this is not the case for everyone.