Hello, Al. No rain, ugh! Sounds like here until 4 days ago! I would surmise that the plant is undergoing transplant shock aaand needs more water.
Wilting of leaves is a plant mechanism that hydrangeas use when they perspire moisture faster than they can absorb water thru the roots. It is very common in the summer months, on windy days, and should eventually be reduced when the plant becomes established in the garden... another way for saying once it develops a bigger root system that lets it absorb more water faster. Right now, its root system got pruned so the plant would fit into one of those plastic pots so, when it is hot or windy, it cannot get enough water as fast as needed.
Wilting episodes typically look bad but the plant should be able to return back to normal in the evening provided the soil is moist. If the soil is not moist, I then immediately add it 1/2 to 1 gallon of water from the crown outwards. Remember that its root system is mostly near the crown so try to water from there outwards. If I see a very bad looking wilting episode, I immediately water but if it seems like it is "the usual", I use my finger to ck the soil moisture and water only if dry or almost dry.
To determine if the plant needs to be watered, insert a finger into the soil early in the morning to a depth of 4" and determine if the soil feels dry, moist or wet. If it feels dry, water the shrub. If it feels moist, skip watering. If it feels wet, you may want to check why (did it just rain? or did the sprinkler go off? or is there some problem?).
On a new plant, I start with 1 gallon of water per watering in Spring. In late May, we get into the 90s here so I increase the amount of water to 1.5 gallons. In July, we hit daily 100s so I tweak things again. By the end of September, I reduce the waterings back to Spring levels. And once the plant goes dormant, I water it every two weeks if it has been dry (the soil does not freeze here). But note that prior to watering, I use the finger method to check if watering is necessary. Since it was planted just two weeks ago, you may want to keep an eye on soil moisture during the winter too as the leaves will eventually brown out, wilting episodes will not occur and you will not notice when it needs water. Keep the plant well mulched year around to help conserve moisture; about 2-4" of organic mulch up to the drip line is fine. I use hardwood mulch but others are fine too.
The finger method can be used daily for 2-3 weeks. Each time you water, you can make a note on a wall calendar. After 2-3 weeks, review the information on the calendar and average out how often you were watering. For example, you may have been watering every 3 days, every 4 days, etc. Then set the springkler to water the shrub 1 gallon of water per watering every 3/4/etc days in Spring (or 1.5 to 2 gallons in the Summer). The amt of water will vary based on winds, weather, type of soil and how fast it drains. It would be nice if when you watered, the water got down to about 8" of depth. Hydrangeas have tiny roots in the top 4" that absorb most of the water so try to keep the soil there as evenly moist as you can with the finger method. If your weather changes or the temps change 10-15 degrees and stay there, consider rechecking with the finger method to see if you need to tweak things.
The amount of sun sounds fine. You can probably give it summer sun until 11am-ish with few problems. In the Spring, the sun is "weaker" so it does not matter if it gets more sun than usual. Same thing happens during the Fall and Winter. Hydrangeas (mopheads and lacecaps) like morning sun & after/evening shade; dappled sun; full shade (but bright shade).
I also have black clay soil but I originally amended the planting beds with organic compost and-or composted manure. Still keep adding more of these every Spring but now it is usually just mulch: https://www.thespruce.com/understanding ... il-2539857