If you face the main gate of DHS from the bus stop area, the boat dock will be to the far right. Walk toward the gates, then hang a right before you reach the entrance plaza. It should be obvious that the boat dock is there.
If you take a bus to Epcot, and the bus drops you at Epcot's main gate area (this is true of all resorts except Yacht/Beach, Boardwalk and the Swan/Dolphin), you cannot access the Epcot resort area without walking through the park. You will not be allowed to walk through the park until the official opening time. This is why you need to go to DHS, because you do not need to enter the park to get to the Epcot resorts from there.
The boat ride will take 15-20 minutes and that does not count the amount of time you might spend waiting for the boat to arrive.