Yeah, where I come from, and what I've read on the internet, you water in the evening. When it cools down, they can regenerate with water and nutrients from the hot summer day. You don't have to worry about moisture at night; there's air circulation outside when they're standing freely.
I'm assuming it's high summer here; if you only watered in the morning, everything would evaporate during the day, and they wouldn't have anything to recover with at night.
This way, you have something in the cool night that doesn't evaporate as quickly and at the start of the day.
But at 30 degrees in the shade/40 degrees in the sun, you wouldn't just water once anyway, but I would also suggest a shady spot.