As you exit DHS, the buses will be on your right, the boat dock on your left. You will see it if you are looking for it. If the boat is there, or just arriving, then it should take about 30 mins to get to Epcot. But, if the boat is just leaving as you get there, then you can safely add another 20 mins until the next boat gets there. Once you get on the boat, it will stop at the S/D, then YC/BC, then BW and finally to Epcot...that takes about 25 mins from DHS dock to Epcot dock.
Or you can walk. Head to the left, same as for the boat. But keep the canal on your left, with the parking lot on your right. The path will head down, towards the canal. It goes underneath the road, then you'll come to BW. If you cut through BW, at the clown pool area, you will see an underpass/tunnel type thing. Go through there, go to the left and then when you get on the boardwalk, go right...keeping BW on your right, the lake on your left. Epcot is about 5 mins from BW. The total time to walk it is about 20 mins. I know that I have left Epcot at the same time the boat did..it beat me to BW by about a min but I got to DHS before the boat came into view around the bend. As I headed to bag check, the boat could be seen.
As already noted, there is a bus to the front of Epcot from DHS.