You should water when lights are ON. If they are on 24/7, then you can pretty much water whenever you want. I like to do it early because my room gets a little hotter in the afternoon, and that helps evap more of the water on the soil surface.
yah when its 24/7 water whenever they need it but dont over water, and you should foliar feed when the lights are off once youve got your plants on 18/6
ok thank guys, i jus seen somewhere it was said to water when the lights were off to prevent the leaves from burning. i suppose this is more of a case for when the plants are under the hps rather than the less intense cfs!