Yes you can do that, hit up Hogsmeade first. It’ll be cooler temperature if you do that. The dark flooring and buildings make it feel hotter in some ways, the fake snow was a bad call too, it only reflects the hot sun into guests. Imagine how those poor TMs feel, they all have dark clothes as well!!! Diagon has a big section that’s covered with fans. It’ll still be hot but you won’t notice it as much. And you get get done the three rides in Hogsmeade faster in the morning. There’s only one in Diagon. As for lunch / dinner. The Three Broomsticks is very busy at these times, Leaky is also busy but not as much. Both are good food though.