Eden got it right. By time, it's usually say a 30 minute race for beginners. After the first lap the officials figure out how many more laps can be fit into the time frame, and start counting down when there are three laps to go. All riders finish on the lead rider's final lap, so if you get lapped, the lead rider (and any non-lapped riders) may have done 5 laps, but the lapped riders only did 4 laps. Does that make sense?

Chicago races take place in parks in the greater Chicago-land area, so they're mostly grass and dirt. One race that I remember from last year had a twisty section as you came down a hill (I don't know the technical term), which mtb riders handled better than roadies just because of their bike handling skills.

The more experienced riders tend to do 45 minute races and they allow hand ups for water. But, I don't think many people do it. Some people do wear camelbacks, but not many.

I could be wrong, but I think some of the 'cross culture is the "suffering" and if you can't drink water, that adds to the suffering.