I would like to point out before anyone freaks out.
Sometimes chams will be awake before lights come on, and be asleep before lights go out.
if they can see sunlight from outside, and the sun goes down, they will sometimes be asleep.
Now, if the cham is sleeping in the middle of the day, that is bad.
But if they are asleep an hour or so before lights go off, more than likely it is nothing to worry about.