Month 5 of trying right now, but still not sure if I even ovulate (have only been using OPK for the last 3 weeks). Still have completely messed up cycles because of BCP.
So as you've probably guessed from reading the replies now, it really depends on the person. Some fall pregnant the first month, others take over half a year to even get their cycles sorted out after birth control pill (me! never going back on again).
Good luck TTC!