You should be able to make it. It will take you a fair amount of time to exit the Fanstasmic area though! There aren't any buses to any of the Epcot resorts from DHS. Your options are.....bus to Epcot, from DHS, and then walk to the WS from the front of the park. Or.....boat to Epcot from DHS and enter WS at the International Gateway. Or...if there is no boat in sight, just walk it.
If you choose the boat option...the boat will go to the S/D first, then YC/BC, BW and then finally to Epcot. It takes about 25 mins. You could hop off at the YC/BC dock and walk to the IG from there..might save a few mins.
If you choose to walk (again, no boat at the dock, or coming into the dock)...exit DHS, keeping the main bus area to your right, the canal to your immediate left. Head to the left when you get past the large open area...the parking lot is now on your right, canal still on the left. A bit down the sidewalk there will be a sign, pointing down a small slope, to the BW area...take this walkway. When you get to the backside of Luna Park (pool area for BW, with the big pool slide) you can cut through. Enter the pool area, with the building on your right, the slide on your immediate left. Walk through the pool area, and to the main bldg..there will be a tunnel. Go through and out to the Village Green. Go left to get to the boardwalk, then right onto the boardwalk (you can see all of this as soon as you come out from the small tunnel). Stay on the boardwalk, go up the incline, and over the bridge, go right and you're at Epcot/IG. The walk takes under 20 mins.
It's really very easy. I almost always walk it vs taking the boat.
I would be out at the bus stop early....by 6:30! This is when the buses start running, but they tend to run a bit less frequently than the normal resort to park buses. If you miss one, it could be almost 25 mins before another one comes along. When you get to MK, I would just walk over to the CR. By the time you walk to the monorail platform, wait for a train to come, then ride to the CR, you could already be there by walking. The only time it's faster than walking is if you really walk quickly to the platform and either the monorail is sitting there and you get right on and leave, or it's just pulling in and you have little to no wait.