I would allot an hour, bearing in mind that the trip could take less than a half hour. You can never be sure how long you may need to wait. I have waited more than 30 minutes for a boat, though it normally doesn’t take that long. You won’t need to transfer boats; one boat makes stops at Epcot, DHS, Boardwalk, YC/BC, and Swan/Dolphin (not in that order). If the weather is good (not too hot and not raining) and you are able, the walk from Epcot to DHS is not what most people would consider short, but is nice. The walk will take you by the Boardwalk (or YC/BC if you prefer) and along a waterway to DHS and should take you a lot less than an hour, even at a leisurely pace.