We went on days that were 7 and 8. Honestly, I just went in with the expectation that it would be crowded and hot. It wasn't as hot as your days, but we had 84-86 a few days. We did what you are planning, arrived as early as possible, left after lunch and came back at dinner. With rope drop, genie, mobile order quick service meals we did amazingly well. The park was very crowded but didn't feel crowded in regard to lines. We didn't wait more than 15 min for any ride. All our food was mobile ordered and ready within 5 min of our arrival, often already ready for pickup when we got there. The only time it felt crowded was navigating around the parks. Tons of people in the walkways, especially the bottleneck areas. We brought misting bottles, cooling towels and UV umbrellas. We only used the misting bottles one day. The biggest help was taking a break in the heat of the day. We'd get back into the AC, shower, nap and rest. Stay hydrated too, I intentionally drank a lot of water to be sure I didn't get overheated and dehydrated.
The 8-10 am time was amazing, we could get a lot done in that window while also using up LL with Genie. We did 9+ rides in 8-9 hours in the parks each day. I know some people might want to get more out of it, but we took a long break in the afternoon and weren't rushing from ride to ride. We'd enjoy a break to eat a snack and rest and we did shopping. We caught all the nighttime shows (didn't do any dining packages for those).
Use your break in the afternoon to strategically stack up LL for when you arrive in the evening. I would use the 12-4 window to snag evening LL for rides, so when we arrived back at the park, we'd have 2-3 LL already loaded up plus an ILL on top of that. This is key because the LL return times will start to push out later and later as the day goes on.
Without Genie, without arriving early at the parks, we would not have gotten as much done and probably would have had a miserable trip. But we had a fabulous time!!
