This is a pleasant walk, and we have done it several times. I would say it takes 10 minutes at a comfortably brisk pace. If you have missed the boat and the weather is pleasant, I would definitely walk, or at closing time at mgm when the boat line is huge, do the walkway, it is definitely faster and very peaceful.
It took us about 20 or 25 minutes to walk from MGM to the Yatch Club. We beat the boat to the dock, when we walked out of MGM there was one boat just leaving and a loooooong line for the next one. MGM had just closed so everyone was headed back to their hotels. We had gotten just past the Swan and Dolphin when the next one came to pick up the group that was waiting when we left.
It was a nice walk, I would recommend it, especially if there is a line waiting for the boats
hi: the walks to epcot and mgm are (imo) definitely better than the launches. what a great way to work off some of the extra calories. we haven't taken a launch to mgm since they reopened the walkway.