Dogs should not be crated for longer than eight hours at a time, and quite a bit less for younger dogs. If you're concerned that your dog may be spending too much time in the crate, you can always try testing to see if he can be left free in the house. Try leaving the house for five minutes and go for a walk. If he's fine with that, try it again at ten minutes and so on. Otherwise, you may want to consider a dog day care or day camp for your dog or even having a dog walker come to your house in the middle of the day to give him some attention and exercise.