It takes roughly 20 minutes to take the boat (after it has arrived) to the Boardwalk. It is a 7 minute ride to the Swan/Dolphin stop alone and there is also the Yacht/Beach Club stop after that. It would be faster to walk, since that only takes about 15 minutes at a slow pace. The boats leave for the last time about 30 minutes after the parks close. After that, you will be forced to walk. There are no busses from MGM or Epcot to the Boardwalk. If you go after Fantasmic on a night where the park closes right after it, you will have to walk back to your car. If you are taking the resort transportation around, you will have to go to Downtown Disney to get back to your hotel.