Timers have little time dials, with one peg for every 24 hours. You push down the pegs for when you want it on, and then poof... anything connected to it is either on or off depending on your timer. If you wanted to be weird, for example, you could have it turn on and off every half an hour. Definatly an experiment to be tried there; not sure if I want to waste a crop on playing around with a timer though.

Anyway, get the best and strongest timer you can buy. Most of them are cheap and work fine, but if you add more lights and fans, they'll all connect through the timer. Or, you can have multiple timers. I don't like that idea very much, because when everything is supposed to be "on", everything should be "on". No weird ten minute period where one side of the room is on and the other side isn't.

Wall power ----> Timer -----> Lights (and maybe fans)

WalMart sells one by GE for a few dollars that's listed as "tough for major appliances". It has a grounding hole, which is nice. Meaning there isn't just the left and right flat blades, but also the center prong for carrying ground. I think that's pretty important if you're going to be having all kinds of crazy lights and fans, both of which create plenty of noise which should be grounded.