Any ideas when the most accurate time to take my pregnancy test would be?

So heres the deal, I am TTC and ovulated on the 11th of May. 4 days later than I should have actually ovulated. I BD every other day to every day this month and on the before during and after ovulation. Anyway, my period is due on the 20th. Like I said Ovulation was last and 10dpo wont happen for me until the 21st..So is it safe to say that I should test with morning urine on the 21st if af is a no show on the 20th? Is that long enough for my pregnancy test to be positive if I did actually conceive?