If its a larger breed (larger bladder) you might be able to leave it for longer but 3 hours is a but much for a pup I think. It does depend on what they get used too and if they have alone time early on then that's what they will think is their normal. The suggestion above of a play area above a crate is a good one as well.
Don't waste too much money on toys in case your pup doesn't like them and just prefers teddies, I learned that the expensive way.
Please do NOT leave a pup alone with soft toys they can easily choke on them. Chew toys that cannot be destroyed are far more suitable. Try a stuffed Kong for youngsters.
