7 hours seems a little light, 10 might be OK.
But it all depends.
In my experience, for CAT 5, don't worry about it too much. Get out there and do your 10 races. Get the experience and feel for the riders in your area. I am not sure where you are racing, pack size and the fitness of the riders plays a big difference. For example, racing in NYC, the packs were always pretty large (expecially CAT 4), but the fitness ranged vastly. It was hard to podium, but somewhat easy to stay with the pack. Go to Boulder, CO and generally the riders are much more fit and have better skills and 10 hours a week of riding will not cut it.