When to start testing with opk's

[Newstart20]

I am using clear blue advanced for the first time this month and wanted to know when is the earliest I should start testing? My cycles are quite short so I'm worried about leaving it too long and missing ovulation. Equally I don't want to waste the tests as they are pretty pricey!

I’m using this for my second cycle and I have a long cycle. Started on cd11 first month and then cd13 this month so if you have a short cycle I would suggest starting tests from cd7/8 especially until you get a bit more info on when you usually ovulate using these tests.

Thanks, tomorrow is CD 7 so that's what I was thinking as I didn't want to miss anything.