So how long after af do I use clear blue digital opk

Preparing for cycle #4 😂😭😖. Have no idea how to use them so all tips and advice are welcome. With the help from glow I have come to realize my cycles are all over the place so my O day probably is too....HELP!!! I this will also be my last cycle tracking because I'm driving my husband crazy so I hope they work + the preseed. Do you test different times of the day?

I met a girl that said it was tough because she tested positive then like an hour later she tested again just to see if she could squeeze in one more round of bd, but the solid face was gone...She had to set an alarm to catch her O and tested at 3am! Is it really that tough findings your o day?