What is your zone? Where are you located? Afternoon shade is always best. New hydrangeas need a few years to establish.

Paniculatas like QF can handle more sun than the ES and they can be placed in full sun is most locations; however, that still does not work well in the extreme southern states. In Canada and the northern half of the US, paniculatas can be enjoyed in full sun.

The leaves of ES suffer more and wilt more than QF's but, this being their first summer, they will definitely wilt during the worst days of the summers.

In my area, we get weeks or months in a row of 38C weather so they suffer sometimes. Although I have drip irrigation, I hand water with a hose on Sundays and maintain mulch about 7.5 to 10cm. All of these guys should recover on their own if the soil remains moist and well mulched.

I`m in Ontario, Canada. I think it is zone 6. The hydrangea in the front of the house which is in afternoon shade is doing just as poorly as the hydrangeas in the backyard which get afternoon sun.

Keep your ES very moist to compensate for the extreme heat....as luis_pr said, they suffer more in the first year they are planted until they become established
I wouldn't worry, your plant will be OK as long as you continue to keep it hydraded.....remember to protect the canes this winter with leaves to prevent die back from our hash winters....

The problem is called transplant shock. It occurs when a plant has its root system cut to fir into one of those plastic pot and then it is moved to shaded place in a plant nursery for selling and then moved again to an outside garden where it is subject to nice temperatures until summer arrives. At that point, the roots cannot deliver as much moisture as fast as the leaves loose it.

It happens always during the first summer and sometimes by the second summer. There are places like mine where I see it every summer because it gets too hot for too long but after the plant becomes adjusted, the number of wilting incidents goes down considerably.

Just keept them moist, well mulched and do not fertilize them. The potting mix probably came with some of those round fertilizer pellets so that should hold them for the whole year. Besides, you do not want to fertilize stressed plants.

You should have seen how sad the ones I have looked until the weather changed and turned cooler and wetter. Our triple digit temperatures (>38C) sapped even my pooches energy. I had to get all outside work done by 10-11am. If I did more than that, I would be drained in the afternoon.

Stay cool.