Ovulation day?

Hi all, I'm on month 2 of TTC and today is CD18. I started bbt this cycle and using opk too. I got a postive opk on CD16 and CD17. I'm unsure of my bbt results. I'm trying to figure out which day I should count as ovulation day. Glow and Flo apps say it's CD17 so according to them I should count today (CD18) as 1DPO. Or, because I got a postive opk on CD17 too, do I count today as ovulation day and tomorrow as 1DPO? Just want to make sure I'm counting correctly. Thanks for any help!