I just returned from 8 days at WDW.
I always forget how LONG everything takes at WDW, especially commuting. It eats up a LOT of time.
We did the following, and other than a couple very warm evenings, had a quite enjoyable time in the parks with temps in the 70s:
Woke up around 10am. Late breakfast around 11am. Hung out at the resort: pool, arcade, movies in the room. Late lunch at the resort or snack in the room.
Around 3:30-4, head out to a park. Most days, it had already stormed and clouds had moved in for the remainder of the evening, dropping temps about 20 degrees from the earlier highs. Some days it was raining at this time. Ponchos on and we walked into mostly empty parks. Some days, it was actively storming. No problem, because I had lined up indoor attraction
Genie+ times as I sat at the resort all morning/early afternoon. I stacked rides, overlapping each other in time so that we had a "plan" every afternoon/evening. I did it in a way to minimize criss crossing the parks. We did just CS meals for dinner, most nights around 7:30 or so. We stayed at parks until they closed, most nights. I felt we had enough time to do everything. We ended up going to the parks on 7 days. We rode numerous things multiple times, got on all the headliners, etc.
We planned our sit down meals as brunches at resorts. A couple days, we drove offsite for lunch as well.
It worked out well and we were never too hot, thanks to the rains that brought relief every evening.
That said, we are done traveling to WDW in the summer. We will no longer be tied to the school calendar starting next year, so we have decided to travel on cooler months going forward.
I will also say, I was out a couple mornings doing laundry and other stuff, and found the humidity at that time to be oppressive to the point of miserable. Even though temps were upper 70s, low 80s, it was stifling. Those same temps in the evenings with the sun low and the cloud cover/rain was FAR easier to tolerate. It felt downright cool several nights. It often got very breezy as well. I will never advocate for early morning park touring in the summer. It's terrible. Take advantage of your empty resort pools at that time while everyone else is sweating it out waiting for rope drop.