No, generally speaking a ferry ride does not save any time. It does add a unique and picturesque element to your trip since you’ll enjoy an experience of Lake Champlain to your itinerary. There are two ferries crossing Lake Champlain, from Grand Isle and Charlotte. Here are links to schedules and other information.
http://ferries.com/vt-ny-ferry-routes/grand-isle-vt-to-plattsburgh-ny/
http://ferries.com/vt-ny-ferry-routes/charlotte-vt-essex-ny/