Yes, you make your reservations once you are on board. Check your navigator for location and time; sometimes they take the ressies in Palo's, sometimes other places. The usually start around 1:30 I think - but check the navigator to be certain.
You can sign up for all 3 (brunch, tea and dinner) at the same time - not sure about repeat visits; I think you can do this but you have to go on a "waiting" list, as they want to try and make sure that everyone who wants gets to try.