12 hours is better than hourly, but ideally I'd set Time Machine to back up when I'm asleep, once a day--mainly because I set my TM to backup over wireless to another machine's external drive over an 80211g connection (I suppose if I had 80211n it wouldn't be as bothersome). Sweet none the less.
TimeMachineScheduler
set Time Machine's backup interval from 1-12 hours
Version: 2.3.1