Confused? Please help

So I have been on birth control for almost a year now. I've always taken it every day. The only thing that changed was the time I took it which didn't vary much. I always took it in the morning around the same time. I took it late in the afternoon on Saturday. But I can continue to take it in the morning Sunday and Monday and Tuesday which is today. I'm supposed to start my period but nothing came today. I have always been on time and I'm curious if taking a pill late one day affects its effectiveness.