As smacky1 said, the unknown is how long the wait for the boat to arrive will be. It takes just about an hour for a boat to make one round trip down to EPCOT and back. My experience has been that the average number of boats in service is either three or four (depending on the crowd size and the time of day). The most number of boats that I've seen has been eight (at Christmastime last year). If eight are running, the wait between boats is only 7 minutes but 15 minutes (for 4 boats) or 20 minutes (for 3 boats) is more realistic. You can kind of get a feel for what the wait situation is by seeing what's going on at the dock. But do get off at the Swan and Dolphin. Otherwise, the walk is very nice (assuming that your feet aren't already worn out!).