I used to turn my fans off at night but it lead to a big increase in night time humidity. I run them 24 hours a day now, and at night my humidity is no different than in the daytime.
I keep my blowers going 24/7 otherwise my temps get too high (texas heat sucks). Probably would be less of a problem if my dark cycle was at night, but I have it swapped.
i turn mine off,although i'ed keep them on if i could....doesn't seem to hurt them tho,i make sure i keep them on till all the left over heat clears out of the box and some fresh air gets in...
i was told:
plants produce CO2 during sleep(dark) cycle so it's best to stall the exhaust vent for first 15 - 20 minutes when the sun rises every DAY. works wonders!!!
but if you're incorporating a window unit AC drawin air from the fresh outdoors then i wouldn't bother
Plants do not need co2 at night, the wind may stop blowing at night but plants in the wildlife are not cooped up in a room. Plants need to transpire at night,air circulation helps this process. Suerte JK