here is another link if you go down to ? 9 you can see the safe time to leave in a crate.
http://www.pettoysplus.com/index.asp...20#stayincrate 9. How long can my pet stay in the crate?
Don't leave your very young puppy in his home all day. At six weeks, a puppy can hold his bladder about four hours. By eight weeks, five hours. By 12 weeks, six hours and by 5-6 months a puppy should be able to hold his bladder for an eight-hour work day.