I guess it all depends where you are in Epcot. If you're in World Showcase, I would just walk over to Boardwalk and take the bus to DS from there. If you're in the front of Epcot, and it's after 4pm, you can take a bus to DS.
Of course, you may be looking to take a boat ride. So, from Epcot to SSR or OKW, figure on 45 mins. It could be more, could be less. Disney says to leave 90 mins to get from point A to point B. It's seldom that long. From SSR or OKW to DS, by boat, figure on 30 or so mins. You may have a wait for the boat...I believe they run every 20 mins or so, then it's about 15 mins on the boat.
You just can't tell what wait times will be, which means having timer on the side of longer travel times.