The Friendship boats make continuous loops througout the day between the International Gateway entrance/exit of Epcot to the Disney/MGM Studios. Along the route they stop at the Yacht/Beach club resorts, the Boardwalk, and the Swan/Dolphin resorts. I agree that they run something like every 15-20 minutes so if you just miss one it's a lot faster to just walk. It is a nice boat ride if you are not in any hurry, or if one just happens to be loading when you arrive at the dock.
The trip from Epcot to the Studios is probably around 20 minutes.
The walk between the two is almost the same, depending on how fast you walk.