When to start OPK

Okc so I've been asking a lot of questions lately but I really like to get input from other women who have been trying. Just wondering how many days after my period I should start using PPL strips? Technically this wasn't a real period it was the withdrawal bleed from my BC and I only bled Tues-Wed. Technically I wouldn't start my new pack until Sunday so my body probably won't even realize I'm off BC until then.