Now is a stressful time to be planting hydrangeas but before we talk water, you may need to transplant it to a location where it gets afternoon shade. In the warmer zones, the leaves suffer from too much sun exposure when allowed to get sun all day long. It is ok to be in full sun in the northeast, for example, but not in the lower half of the country. Whee I live, I try to provide shade starting at 11am-12pm.

Mulch it with 3-4" of organic mulch and give it about 1 gallon of water per watering (1.5 gallons if your soil is sandy). Use the finger method daily in the early morning to determine when to water. Then after 2-3 weeks, review how often you water and set the sprinkler to give it 1 gallon of water on the same frequency (every 3/4/etc days). It may help to note in a wall calendar everytime you water.

Wilting will be a problem during the summer months on during windy days. It will be less so once the plant becomes established in 1-2 years.

If you see a wlting episode, insert a finger to test the soil. If it feels moist or wet, take no action. The shrub should recover on its own by the next morning or before. If the soil feels dry, water it.

If you notice that the leaves are turning brown from the edges inwards, the plant needs water. If you notice that the blooms are browning out, it may be getting too much sun.

Are they mopheads? Paniculatas?

If you don't want to move them you can rig a dandly shadecloth with a couple of stakes, a sheet, and a handful of clothespins. Just to get them through the transplant phase.

And of course next year do your planting much earlier.

Direct, all day sun in zone 8 or above for any macrophylla is going to be an extremely stressful situation. These prefer (and some some cases, require) morning sun and afternoon shade.

Paniculatas are far more sun tolerant but even these can be stressed if very new plantings. A mid-June planting in zone 8 of pretty much anything is asking for some transplant shock. Just keep everything adequately watered and the rigging of temporary shade shelter as noted above can be helpful.