Rebecca:
Thanks for the question!
Generally, Chip 'n' Dale's campfire singalong at Fort Wilderness begins at 8 p.m. during Daylight Savings Time--and so in August that's when it will begin. You actually won't have as much time as you think since the dinner will get out around 6:45 p.m. Give yourself at least 30 minutes to either walk from Pioneer Hall over to the amphitheater or take the Yellow Line bus from Pioneer Hall to the 1500 Loop drop off for the final 100 yards to the campfire. You can visit the Meadows Trading Post or take some marshmallows to roast when the firepots are lit at 7:40 p.m. and get a good seat.
You may want to kill some time AFTER the campfire, as it ends at 8:20 p.m. The Electric Water Pageant performs at the fort's pier at 9:45 p.m. and then, of course, there's the Magic Kingdom fireworks you can see from the pier, also. Fireworks at the Magic Kingdom vary, so you'll need to keep an eye on the
calendar at www.disneyworld.com and work it into the schedule. (The schedule will be up 3 months out.) There's a playground near the pier along with the stables around the back of Pioneer Hall to enjoy. I don't think you'll have a hard time finding something to do while you wait!
Wishing y'all a magical vacation!
Whitney