This is the first time they are making a "stop" at WDW as part of the cruise price. Typically, the ships leave from PC, so they are sailing out by 4 or 5pm. But for the NY cruises, they are making PC/WDW one of the Port of Calls. The buses start taking passengers to WDW at 7am, at various intervals through the morning. "all aboard" is 11pm (I think, I would need to check the cruise documents we just got
) They are most likely in no hurry to leave, because the next 2 days are "sea days" so they aren't trying to get anywhere in time!
Yes, you do have the option to stay aboard for the day, or there are excursions to NASA too. Some people have no interest in going to WDW for just one day. But, the Park Hopper pass is part of your cruise price, along with the free transportation. Guess we'll see what people start saying about this port of call, I am re-thinking going for one hot day in June! And, I hear Obama may be there the week we are there...even more crowds and nightmares (they block off areas and stuff).
Hope that answers your question!