I have had varied + results on OPKS, check out my charts. Some times i just have one positive and other times i have many +. One month i had those pale ones you have written about for a week, then a darker positive.
What brand OPKs are you using? Ive gone to the extreme of using 2 diff. brands at the same time to double check what is happening. I know there are some people who dont have any success with particular brands.
As for the timing of testing, i usually test in the afternoon due to work committements but if its a weekend etc then i might test a couple of times.

Good Luck