you can your period at ANY time during the placebo pills for it to be considered on time, it normally takes 2-3 days for the body to register a drop in hormones and begin bleeding, but its all a matter of body type.

Most women end up bleeding between the 2nd and 4th day of placebo pills. However, it can happen any time during those pills, and even sometimes women can skip a period. If you have been taking your pills on time you should be just fine and not pregnant.