I've left the boat dock area, International Gateway, at the same time the boat left. The boat CMs yelled that there would be another boat there in about 15 mins...we yelled back that we would beat them to DHS! He laughed at us. The boat was at BW when we got to that dock. We cut through the pi area, Luna Park, as the boat was leaving for YC/BC. We didn't see it again until we were headed to DHS bag check and the boat was just rounding the corner, coming into view. We beat the boat by about 5 mins.
We do walk at a decent pace. It usually takes us about 18 mins to walk between the two parks. But...if it's brutally hot or raining, the boat is a better bet, even if you do have to wditvup to 20 mins for the boat to get there!!