It depends on when you want to get to port. We have a tradition of trying to get there when it opens, get in line, then head up to the Goofy pool. The girls are the first in the pool, and DH and I get pizza for lunch (I know they have the buffet, but we are fine passing that up so that the girls actually get the pool to themselves that one and only time on the cruise each time).
So we leave WDW are around 9:00 am to head over to get us there around 10:30 when they start letting people in. but you don't have to be at port until aroun 3:00-3:30 if you want to come later (but lunch will be over by then). So I would say to plan for 1 1 /2 hours to get there (maybe take less time depending on traffic and finding your way) and plan to be there between 10:30-3:30.
A for when you get off the ship, I think they start letting people off around 8:00 - 9:00 am on Saturday morning.
DJ