Could it be a squash bore? I have bush varieties of zucchini, acron, and butternut, and one of my acorn bushes has wilting yellow and dried up leaves just like you described. I've had issues with them before, but I'm not sure if they affect "bush" varieties.

Possibly bacterial wilt, which is spread by striped cucumber beetles. If so, there's nothing to do that I've ever heard about. Everything I've ever read says that if it's bacterial wilt, just pull out the plant or the disease will spread to other plants.

Some varieties are resistant, particularly acorn and butternut among winter squash. I don't know about summer squash, but last year the wilt killed my zukes, but my yellow crooknecks were fine.

I hope it's not bacterial wilt -- that's one nasty disease.

Google "bacterial wilt squash": you can find the various symptoms, info on resistant varieties, etc. Good luck.

Wilting in the heat of the day is a normal response for many plants -- including squash. Resist the temptation to over water as you may invite powdery mildew and other problems. As long as the plant recovers when the temp drops back down you're OK.