I'd say either yesterday or today for O. I usually assume 24 hours after the first OPK (ie yesterday), but if the first one was picking up the beginning of the surge, the peak could have been on the second day of OPKs, which would put O the day after that (ie today). I would pick one of those two days based on how other signs line up. I know you said you had no EWCM, so the last day of creamy CM could be O day.