To answer your question, you would probably find the typical cycle between 8 & 12 weeks. Could depend on your goals & how you are responding to it. How is it going so far?
As far as interaction w/ B/C - there is none. However keep in mind that many women experience an interuption or irregularity in their regular period schedule. Just because your period stopped doesn't mean that you can't become pregnant.
The usual comment you will get is that B/C by itself can cause some weight gain / bloat and in the situation of preparing for a competition, any birth control pills (including patch or any other artificial hormone introduction) will just be discontinued to avoid that accompanying bloat and fat gain (or lack of fat loss). Thus if the competition prep includes use of any AS, there is no issue with the birth control pill.