When to start ovulation testing?

Bre
I have never really tracked my ovulation so I don't know when it is! I mean, these apps and my cycle length etc give an estimate, but I'm going to try the clear blue opk this month! 
Only problem is... I have no clue when to start it! There is the guideline of CD9-10, but what if I'm earlier? Can I start now? And do I test every other day until I see some blinking happiness? 
My cycles are 31 days, I'm on CD6 (my period ended 2 days ago) and glow puts my fertile window from the 16th. 
Thanks!!!