You could also take a taxi from either the front of Epcot or one of the Epcot resorts. It'd be about 20 minutes travel time (probably less). I would guess fare would be about $20 plus tip.
For the boat method, I would allow closer to 1.5 hours to be safe. The boat ride takes about 20-25 minutes to get from Epcot to DHS. The boats depart about every 15-20 minutes, so if you just miss the boat, it'll be about 15-20 minutes before the next one departs. You could also walk from Epcot to DHS...it's about 1.1 miles.