This may sound like a surprise, but making love only after first getting a positive OPK may not get you pregnant at all. Ovulation can happen as early as 14 hours after the OPK first becomes positive. Let's say you test with the OPK at 8 a.m. and it was negative. Then, the OPK turns positive at 11 a.m, but you won't know because you only test once a day. So ovulation could then happen 14 hours later, at 1 a.m. the next day. But having sex after ovulation is not going to get you pregnant.
The perfect time for sexual intercourse is within 12-24 hours prior to the ovulation predictor FIRST turning positive. This is especially if you test only once a day. It is best to test every 12 hours not every 24 hours.
If you test once only every 24 hours you will only find out about the positive OPK at 8 a.m. the next day, which may be too late for getting pregnant if you only have sex at that time.
Testing every 12 hours may be more reliable to predict ovulation. Making love after ovulation won't get you pregnant, so if you rely on the OPK and you wait to have sex only when the test becomes positive, you may decrease your chances of getting pregnant.
That's why it's generally suggested to have intercourse two to three times each and every week. That way you are unlikely to miss ovulation. In addition, you may want to make love once a day when the OPK turns positive, just to make sure.