I enquired about the sealion encounter direct with the provider for our upcoming 3-nighter. I asked way before the Disney excursion booking opened, and they had no availability apart from 8.30am and I think 5.30pm (so one before you can go ashore, and one too late for all-aboard). I am assuming from this that Disney had block booked the two times that worked out for Wonder guests, as I booked through their excursions when they opened with no problem at all. Kind of forced me to pay their marked-up rates, but this is the excursion we really wanted, so we bit the bullet.
Haven't checked your tickers to see when you go, but if I'm up first I'm happy to report back. There will be 2 of us participating (DD and me) and one observer (DH).
ETA - no tickers LOL. We are on the April 2nd 3 nighter, and will be home from WDW April 12th. Does that help in your planning at all, or is it too late?