Like many things here, there’s no one “right” way to do this. I would completely disagree with those who say that getting there super early, then leaving midday and coming back later is the “best” way to do it. Maybe for them it is, but to me it makes very little sense. I’m not saying we never do that, but we don’t do it pre-planned. If we do it, it’s spur of the moment…we were in the park earlier in the day and went home because we were done. If we eat dinner and decide to go back out, we just do.
We don’t show up until 9:30 or 10:00am. We don’t leave midday, unless that just happens to be when we’re done. Yes, it’s very hot, but that’s the beauty of WDW…you don’t need to be in the heat. A majority of rides are a/c, and even the queue is a/c. So you can spend the overwhelming, vast majority of the midday out of the sun and heat, easily. Just do rides that are indoors, so your only exposure outside is walking from spot to spot. Water rides are also good for midday.
So really, my answer is do whatever fits your style. Don’t let the fact that it’s July influence you too much. The worst of the heat can be largely avoided with some common sense. If you want to do a midday break, great, but it’s not the “best” or “right” way.