I've never gotten to MCO later than 9:45 after a cruise. This usually includes checking in and getting through security. We're usually finished with breakfast before they have cleared the ship, so we hang out in the promenade lounge until they start letting people off. The last time we went, it took a bit longer because we had to get our bags off the bus and then check them in. We were still waiting at our gate before 10:30. Now that they've re-instated bag checks at the pier (or so I'm told), it should be eaisier to check in at the airport again.
I think every bus I've taken has left the pier before 8:30.