When do you use the OPK tests? Missed my window....

I’m TTC for baby #2 and I thought the opk tests were accurate no matter what time of day you use them, is that correct? I know pregnancy tests say to use morning urine but the clearblue advanced digital opk tests don’t say anything.

This app says I’m supposed to ovulate tomorrow but I just took an opk test and it said low so I’m wondering if I ovulated a couple days ago. Thursday & Friday I was having a lot of CM so I should have tested then 😭😭 we only did it on Monday and Wednesday of last week so my chances are low now of getting pregnant this month. URGH 😭😭😭 I’m so mad at myself!! I think with my first baby I ovulated a lot earlier than the app predicted so I should’ve known better. I have always had really short cycles too.