Hello again, Edward! Thanks for sending me this great question.
I love staying in the Cabins at Disney's Fort Wilderness Resort & Campground, but there's a reason they call it "wilderness." Its massive size and off-the-beaten-path location can make just getting around a whole new adventure! I have a couple of suggestions that may help in your planning.
To travel to Epcot by bus, you'll board at the main bus stop at the front of the resort, near the Reception Outpost. You can take an internal bus to get there, but we've found it much easier and more convenient to get around Fort Wilderness by renting a golf cart, which would also save you a little time. Buses officially start running about an hour before park opening, so you can expect service to Epcot to start around 8 a.m. I'd hop in my cart by 7:45 or so and try to be at the bus stop before 8 for one of the first buses out. That would help account for the number of other Guests also catching the bus, the 15-20 minute travel time, and getting through security once you arrive at Epcot.
Alternatively, if you have a car with you, that would be the quickest and most hassle-free way to go. Since you're a Disney Resort hotel guest, you can park for free at the Theme Parks throughout your stay. If you choose to drive yourself, you should probably plan about 30-45 minutes to allow for travel time, parking and security.
I hope this helps you make the most of your day, Edward. Thanks again for stopping by to see me, and I wish your family a magical Walt Disney World vacation!
Keep Disney Dreaming,
Kathy K.