It all depends on the brand. The type I use recommend waiting 15 minutes, so I force myself to walk away..lol. I believe all brands can be read up to an hour though.
Lots of women have to test twice a day...unfortunately that gets pricey I know. I can also tell you, just in my personal experience, interpreting those lines makes me crazy. I am a really big advocate of the ClearBlue digital. Takes the guesswork out of it.
Also, not sure what time of day you are testing, but first morning is not the best. This is because most women will experience their surge starting early morning, but it takes several hours for the LH to reach your urine. I have always found that late afternoon seems to work best. And of course make sure you cut out liquids for a solid two hours prior to testing, and try peeing in a cup and dipping instead of peeing directly on the stick.
Perhaps you are already doing all these things, but thought I would mention them anyway.
For some women the surge is very brief. So you still may ovulate in the standard time after a positive, but miss the positive.
Hope some of this helps, good luck to you!
I would say if you are getting your period then you are ovulating. I would keep doing the opks as you might be testing on the wrong days. Try Cd 10-21 - that is when most O