Hey, as Bluntzilla replied, the fans should be kept on 24/7 so the plant's stem thickens and can support the weight of the buds... what do you mean by the extractors? The exhaust fans and the activated carbon filter? Anyway, the answer is that they should always be on... but I turned it on in the third week because the plant wasn't smelling and it still doesn't (I'm about to enter week 5). To let fresh air into the grow, I left the little windows open at the bottom... I hope I helped you, dear. Anyway, happy growing and good luck with everything. Happy New Year and happy holidays!