Ovulation test tips?

I'm expecting AF by 9-20. I just have a feeling I'm not pregnant. With my son I never really tracked my ovulation with the test sticks (but I have a million). I got pregnant just by plugging my period into an <a href="https://play.google.com/store/apps/details?id=com.glow.android">ovulation tracker</a> app. But time is kinda sensitive and we want to get pregnant ASAP. Assuming AF shows her ugly face next week (but maybe she won't?!?), how long after she's gone do you start testing for ovulation...one week, two weeks? Thanks for any tips! Edit: I realize you typically ovulate two weeks after AF but is it good to start testing a week after to be SURE it's not missed?