Birth control pills are daily pills which are basically of two types. They are the more common combined combination pills which contain two hormones, oestrogen and progesterone and the progesterone only pills which contain the hormone progesterone only. Both can be started at anytime of your period so far you are not pregnant and not at risk of being pregnant in seven days i.e. No recent unprotected intercourse prior to commencement of usage. But for ease of usage it is usaully started at the beginning of your menstrual period that way it is sure you are not pregnant and the chances are certain that you can’t get pregnant in 7 days.