I agree with outdoorsman, morning water so they can concentrate on the sun, has it been windy or in a area where the breeze may be too strong?
I have seen this before on my outdoor grows when I had a dry windy day, it kind of sucked the moisture out of the leaves and the root system could not keep up. My old spot was sheltered pretty good on 3 sides but when we would get a east or south east wind, the plants on the edge would look a lot like yours. The would recover with no issues but they looked like hell for awhile till they did.
The other thing to consider which is the opposite of to windy is no wind, if they get strong hot sun with no breeze, they bake in the sun and the moisture in the leaves is the first to go.
By watching the forcast and adjusting where your plants spend the day may take care of what you are seeing.