Does anyone know which dinner time (4:15 or 6:30) would be best to finish dinner in time to go to the Ft. Wilderness campfire singalong?
It depends.
HDDR is about 90-105 minutes (don't remember) and there is a break in between shows of about 15-30 minutes to get the previous crowd out, clear and reset tables, and prepare for the next show.
The Campfire Singalong starts at 7pm during the winter months (when we turn the clocks back) APPROXIMATELY with the campfires lit at 630pm, the singalong with Chip & Dale starts at 7pm, and the movie starts at about 740pm. During the summer months (when we turn the clocks forward) APPROXIMATELY everything is an hour later.
Since the HDDR times don't move with the clocks, to be safe you should do the earlier show to ensure time to get to the campfire singalong. (TNKim, you didn't say what time of year you would be there). You can go to the Horse Barn before to see the horses that work Main Street and the parades in their paddocks and there are pony rides for kids under 85# (led by the parent) in the corral between the Horse Barn and HDDR. There is a slight charge for the pony ride (less than $10).
FWIW we have done HDDR several times in all categories and there are no bad seats. The performers make sure to come upstairs during the show so nobody feels left out. Last show we were in the balcony directly across from the stage which were great seats (elevated, straight on) plus the food and unlimited beer/sangria is refreshing. Within each category, seat assignments are based when you booked - earlier means closer).
At the campfire singalong, the Chuckwagon that for decades sold snacks, sticks, marshmallows and s'mores kits has been replaced recently by a food truck parked near the movie screen that in addition serves some dinner like items (chicken finger dinners, etc).
If you want more information on Fort Wilderness things, check out and search the DIS Camping Forum at
https://www.disboards.com/forums/camping-at-disney-world.24/
Bama Ed