if your talking about your exhaust fan,then the answer is yes always leave it on to keep getting the air out and it also helps keep the temp down.U don't want air sitting around for to long inside your box
my pops would turn my fan off for a few hours even though i didnt tell him too and it never hurt my plants so if you need to for a some reason it wont hurt it if its not that long..
damn parents always think they know better even when it comes to growing weed