The boat operator (captain? skipper? pilot?...whatever) announced a 35 minute trip from MGM to Epcot International Gateway when I took it last week. You could probably walk it in very close to the same time (assuming no small children to slow you down and that you don't stop at Big River or ESPN Club for a quick beer along the way). Actually, this could be quite a bit of fun, if you left MGM at the same time as the boat departed, since the boat would arrive at the Swan/Dolphin well ahead of you, but then have to unload/load there, at the Y&BC, and finally at the BW before going on to Epcot. I suspect you would arrive at the BW while the boat was still at Y&B and might not pass you as you walk along the canal to Epcot.
Ralph