Plan B

Do any of you ladies how exactly how much a plan B pill will mess with your cycle? I had unprotected sex twice in a night about four days ago, that next day around noon "about twelve hours after the intercourse" I took the plan B pill. My period was supposed to start the day I took the plan b but it still hasnt started yet. Ive always been really super regular.. how long should I wait with no period before I take a test?