Morning, plant use the most water during photosythesis, which happens during the day. Night they are more in rest mode.
Whenever you want to! I usually go with right before the light cycle or right when the lights come on. Other people prefer when they go off. One of my friends swears by it he says the root grows at night and that bitch is thirsty! lol
Before the heat hits..from what I have seen they seem to drink better when you feed then early in the day before it gets hot.