How long can Plan B delay your period?

Im desperate. I had unprotected sex with bf 3 days before I was supposed to get my period. I was thinking the best option was to take the pill not to risk it. But my period is late now. I took the pill aroubd 12 hrs later. I was not near ovulation bc my period was supposed to arrive. Now im really nervouss 😭 how long can my period last to come?