Confused-are birth control pills 99% effective after 1 week? pamphlet says back-up for 7 days but people are saying it takes a month? loestrin 1/20

Not a month: You are certainly "safe" (1%failure rate when used correctly) well before one month. The one week wait is probably sufficient. I usually advise a two week wait, but this is most likely being overly cautious. However, getting pregnant when you don't want to be is a big deal.

A month: Birth control works by preventing you from ovulating. If you ovulated before starting birth control, the egg can stay in transit and still be fertilized despite being on birth control. It usually won't stay viable longer than two weeks, but you can overlap with barrier birth control for 4 weeks to be safe.