No don't worry, if you have the means to provide some shade during those hot hours it will keep them from wilting, here in Texas every single day that isn't overcast mine wilt from 12 noon to about 6 pm then the perk up nice, just make sure they have enough water or they might be bitter, after I started watering a little more my cukes are not bitter or it could be that the first fruit are bitter regardless, I haven't figured that out yet. I would think that if they do not recover or the leaves start to look off color it would be a different problem. Just my observation though I am not an expert by any means. I know that I wilt between 12 noon and 6 pm lol.:o)Deanna

Is it wilt or are the stems near the ground cut partially through. The white on the one leaf looks like sun damage. The other plants look like cutworm damage. Take aluminum foil and wrap the stems with a inch to 1 1/2 inch strips. Not saying the perlite does not work but I have seen cutworms on sharp gravel.

There are 6 species of Cucumber Beetles and they not only will feed on about all of the plants in this melon family but numerous other plants as well. The link below is a good article about them and the methods of control that can be used. There is no one thing that is consistently effective but a variety of methods need to be used. The presence of Powdery Mildew indicates more problems and that you should look at the soil you are growing these in ot be sure it is good and healthy. Powdery Mildew can be fairly easily controlled with sprays of either 1 teaspoon of baking soda mixed in 1 quart of water or a 50/50 mix of fat free milk and water sprayed every 5 to 7 days on infected plants. Here is a link that might be useful: Cucumber beetles

If all of the plants are already infected It is too late to save the plants and they will eventually succumb but it may take several weeks and it is perfectly safe to eat and pickle the cukes as long as they remain sweet. Eventually they will probably start to turn bitter because the plant can no longer supply the fruit.