While the bike trail between WL and FW is now closed for construction of Reflections, there is still plenty to do over at Fort Wilderness once you get over there. You could rent bikes from FW and ride around the campsite loops. Kids love the simple playground near the beach, and there are pony rides for little ones that you don't need reservations for. If you want to go for a trail ride on a full size horse (and everyone is 9 or older) it would be worth getting a reservation for the trail rides, which leave from the opposite end of Fort Wilderness, about a mile from the beach area but you can take any internal FW bus to get over there. The campfire with Chip and Dale is great too, and doesn't need any reservations. It is in the park in the middle of FW, also accessible by internal bus. Finally, we enjoy dinner at Trail's End right next to Hoop De Doo near the beach. It is often one of the easier restaurants to get into without a reservation, and has great comfort food.
As for timing that's totally up to you, but in July it might be best to avoid the heat of the middle of the day. We often end up over there in the afternoon and into the evening, allowing us to catch the campfire after dinner. If you schedule a trail ride then morning might work better, but that's up to you.
Enjoy!