I don't know where you live. So, I don't know how hot it gets. Here, it does get hot, AND very humid. BUT, at 6 or 7 am? It is still VERY pleasant, and it is difficult to imagine where you are living that it wouldn't be the same. I do think dogs need daily walks.

As for leaving them at home? You are talking 5 hours or so, right? That doesn't seem unreasonable to me, really. It seems a teeny tiny bit odd that you wouldn't leave them. You did go to school, didn't you? Without the dogs?