First time using opks

I'm new at using opk test. How soon after you get a positive test do you ovulate? I'm trying to be organized and line them up for each day. I see that it's getting darker today but I know its still negative. I just didn't know if I need to wait until it is positive to BD or will it be too late by then? We have been every other day since CD 9. Just making sure I'm not wasting my time ha ha not to sound mean to hubby lol.