fans off? drooping lights?

Hi there! thank you for reading i appericate it very much. well i have a 3ftx 2ftx 71/2 ft grow room, I have a 250 watt hydro farm light system.I 'am in day 2 of my veg stage.

Plants are 1 purple diesel and 4 power 19s. Plants are about 4-6 inches. My question is during my 6 hours off can i turn off my 90 cfm in/out exchange off or is this crucial to venilation.

Also and sorry but two of my 19s are droping I had the light 17 inches away moved it too 2ft my temp/humididty are 75deg/40% humidity. Is there a reason. Thank you so much for help, would not be wear I'am in growing if not for this site.

best to keep that circulation going all the time. plants tanspire co2 and take in 02 during the night times, albeit, a lot lot than the reverse during the day.
droopage at your stage sounds like overwatering but post some pics. believe it or not, you are better off with fluors during first couple weeks of veg.