New to opks

Hey y'all! This my first month using opks. I got a ten pack of clearblue (not the digital ones) opks and I ordered a bunch of cheap strips that will arrive on the 25th. What day should I begin testing? I've seen some people say that you should start testing a few days after your period ends and the clearblue package says on cycle day 10? My period can be pretty irregular last cycle it was 40 days long. Should I start testing pretty soon anyways? If I need to start testing I thought I could start with the clearblue tests and then when the cheap ones arrive I can take both tests for a few days to see how they compare (or is that completely unnecessary?). Lol thank you in advance!!

(Also I took this screenshot yesterday so it says today is the 20th but it's obviously the 21st🤪)