When should I be testing for ovulation?

This is my first month using ovulation tests so I'm still trying to gauge when I should be doing it. I took the first one on Sunday 31st because on the Flo app the predictions are slightly different, according to glow I will ovulate on the 7th but one of the tests I did on Sunday looks the darkest and they're getting lighter now? I'm not sure someone help lol might be doing it too soon. I'm also struggling to get into a routine of doing it so that's why the times are all messed up