as long as you dont get water on the leaves when the lights are on, you can water then. or you can water at night. i think plants recover at night so i usually water about an hour or two before it gets dark.
what he said i prefer to water my girls in Veg 2 - 3 hrs after lights off kinda like a midnight rain fall as you get into your flowering stage i tend to water when lights go on thus stopping so much humidity build up
IMO no lights, no water, they dont need it during the dark period. The leaves transpire during the light period to cool the leaves. That's when roots need access to water. Just my thoughts on it.
Not going to get into water on the leaves, and optics debate. It rain naturally, morning dew, the plant will be fine, strong nutes on the leaves is a different story.