It depends. Theory of an engine is that valve life determines a lot and the design of the valves is a big factor. I have not seen the setup of the valves for the 450 but w/a dual overhead cam setup I can tell you that 10hrs or less is a little extreme.
In 10hrs your valves should not be too much past the basic seating position. I know C'Dale had like a every 50hrs and I went 330hrs or so w/out adjusting them at all. Of course they were gone when it came to a rebuild but they worked fine. Probably should've been adjusted around 100hrs or so but think of this. When you do a rebuild or after a couple hundred hours, don't most people/dealer switch out for new valves anyway? They are cheap and usually costs less to replace than for a dealer to repair them.
I say when someone gets like 25hrs on one to then check their valves and tell the rest of us w/photos.
I'd do it but I ONLY ride tracks so get like 4-8hrs a month on it at the moment. Granted track riding is a pain on an engine, but it'll take me awhile to get there. If no one does then I'll pop mine out in a month or so just for kicks and check them out. Maybe see what can be done to boost the power w/lighter springs or something anyway.
I agree with Psychosis and since your quad is new you may just want to check them after 10 or 15 hours. I really think you wont have to check them very often but it will be dependent on how hard you ride it. Racing will be the worst case.
I don't have a quad yet but i want to know when the maintenence will be so I can know when I need to do everything but I do think 10 hrs. is way too often to adjust the valves. I think 40-50 hrs. would do it. if it was every 200 miles that could be every 10 hrs. if you go an average of at least 20 mph. could be every four hrs. if you rode 50 everywhere
You may consider bringing your bike back to the dealer for the initial 10 hour maintenance, because if there are is no records of maintenance on your bike it's very difficult to put a warranty claim in if something should happen.
I personally prefer to adjust my own valves, but take it to the dealer only for this reason (after I returned from the dealer I doublecheck the valve lash).