Like she said above, average is 14 days. Some are different. For instance, my friend told me last night that she averages getting her O 16 days after AF, BUT... she got a positive OPK today... 4 days early. I start testing about a week before my O day just in case it changes. According to my FF app, I'm supposed to O on Monday but according to my OPKs it looks like it might be tomorrow.