If you are coming into it with a good road race or mtn bike base then you can do well with only 5-10 hrs of training a week. I turn down the volume and up the intensity.

Recommended cyclocross work-outs

1) Mount and Dismount training… Practice, practice, practice. When I first started racing I would work on my mount and dismount 3-4 days a week. You will loose or gain so much in a race depending on how fast or slow you can get on and off your bike.
2) Quick Start Intervals: From a complete stop with your foot out of the pedal go as hard as you can for 30-60 seconds. Do 5-20 of these with 1 minute rests in between. Come to a complete stop before each one. The start in cross is very important. You want to go into that 1st barrier or run-up top 5. Crashes and log-jams happen on the 1st lap.
3) Cruise Intervals: at your LT (when you feel the burn in your legs) do 2, 10-30 min intervals with a 3-5 min rest in between. This simulates race pace.
4) 1 Minute On 1 Minute Off Intervals: go as hard as you can for 1 minute, rest 1 minute and repeat. Make sure you are ON for 10-30 mins. Cross races can be like road races with drafting and attacking. To move to the next group up the road or to drop the group you are with, these intervals are key.
5) Run: run at a moderate pace for 20-30 mins. Get the legs ready for the little running that is involved in cross.
6) Hill/Stair Intervals: find a 10-30second set of stairs or hill and do running repeats up these. Do 10-20 of these. Or, if the weather is bad, go to the club and hop on the stair-climber and turn it up as fast as it will go.
7) Yoga and Core Exercises: Cross is hard!