birth control has to be atleast two to three months in your system to be on the safe side and not fall pregnant. when i got married i went to the obgyn to get a presription for birth control, and told him i would be gettting married in two weeks time. he told me that i had to start the pill two to three months prior in order for the pill to be extremely effective. for as long as i have been married condoms has always been used. eventhough i am on the pill for almost a year and six months. birth control in my case was also used to regulate my period as it was extremely irregular making my chances to fall pregnant great. it also depends if your on a mild birth control or if you have regular periods..
thats just my take hope it helps
rather just be safe and use condoms from now till after two months or when you feel the need to stop using them. remember to also take your pill regularly at the same time everyday thay also allows for its effectiveness to work