Most opk's tell you about 24 to 48hrs before you ovulate. You should start having sex every other day way before you get the positive.
So lets say you have the normal 28 day cycle..and you start testing on day 11...you should have sex day 11,13,15,17 or 10,12,14,16..
I have gotten preggo 3 times using OPK's and those are the days I have had sex I have a 27 to 28 day cycle and I usually get my positive Opk on either cd13 or cd14...
The sperm can live for days while the egg only 12 to 14hrs so if you have sex before you get your positive the sperm will be waiting for the egg..
As for testing, you can start testing 10dpo but the closer you get to your next AF the more accurate your test will be..so if you get a negative before your expected period dont get discouraged just wait till your due and test then or right after..
Good Luck!
I have used them in the past, but in terms of success....we haven't gotten pregnant b/c we have fertility problems. I can tell you that my fertility specialists has me using them in order to time interuterine insemination, so he must think they are a reliable/valid method of predicting ovulation. As soon as I get a positive test, my doc does a blood test that day to check out my LH level, so I'd assume you can test as soon as you get a pos result.
I can tell you not to bother with charting your basal body temp. I did this for several months for over a year and it was so different every time, despite normal cycles. My doc said they aren't reliable at all. Good luck.