I'm helping crate train my neighbors puppy but there's a few things I don't remember . . .
How long is too long to keep your puppy in the crate? I feel like I may have left my pup for up to 3-4 hours but can't remember!
You don't want to leave him longer than he can reasonably hold his urine, this varies by dog,
in general
3 mos old dogs 3-5 hours
4 mos 4-6