You're in Hawaii, so I'm assuming the temps are already pretty high. My experience has been this is a plant's response to the heat of the day: they droop (not wilt), and as long as they have recovered by the morning you're good. I imagine it has something to do with water being lost from the leaves at a rate higher than the plants are able to take in from the soil, so the plants are unable to stay erect. At least, that's what I would assume.
Anyway, point being, perfectly normal.
(If you feel the stems when they're droopy they should still be somewhat firm; unlike the limp stems and leaves you find on a wilting plant)