The pathway starts behind the Boardwalk Resorts and takes 10 - 15 minutes depending how fast you walk. We used it several times to save time because the boat ride can easily take twice as long.
Just got back, we stayed at BC but walked over to Dolphin for breakfast at Coral Cafe, then walked to MGM because we just missed the boat. We thought it was a pretty long walk, about 25 minutes or so.