We took the skyliner from DHS to the International Gateway once on a recent trip, primarily to get the Skyliner ride and not to save time. It did take about 25 minutes and was fun to do once.
Depending on your walking speed, if you don’t want to walk the whole way but want to save a few minutes, you can take the boat to either the Swan and Dolphin dock or the Yacht Club dock and walk from there. From the Yacht Club you should be able to get to the IG in less time than it takes the boat to go across the lagoon to the Boardwalk and then to the IG. We often do that on hot days.