I don't know what fans you are talking about but if you are talking about oscillating fans it'd be good to leave them on during the entire period of the lights being on. If you're talking about exhaust fans and such I dunno, never used em.
orangeman Reviewed by orangeman on . fans on timers can anyone tell me how often my fans sould kick on, and for how long? i have a 400 wtt mh in a area about 8x8x8 i have 20 plants and two e-z clone 120 (no clones yet):thumbsup: Rating: 5