OPKs are charting the increase in a hormone that peaks just before you O. So the few days of + OPKs indicate that you are close to ovulation, ITMS. It drops once you have O'd. So I would go by CD17-18. It can take 24 hrs or more for O to occur after the surge. Did you get any twingy O-type pains on CD17 or 18? The temp spike would also indicate O (the biggest one, that is). I never temped, but I charted CM and used OPKs for DD2. I only used OPKs for one month. It worked straight away for us. GL with your TWW!