From what I understand with OPK's you need to test later in the day as that is when the body releases the hormones. I don't have any instructions in front of me but I remember something written to that effect. I'm sure 8pm was noted as an optimum time. I used them for a couple of cycles and never got a truly dark line but it did get darker over 3 days IYKWIM.

Testing three times a day would be unnecessary as well as expensive. Hold off and do one test later and then BD as required

Also what other methods are you doing? Temperature charting and CM observations can help to pinpoint what is going on if you're unsure.