
6 hours is quite reasonable for a young pup, just like human baby.
On the other hand getting so stressed out that he screams for hours is not good for either of you.
Are you leaving a radio on so he is not hearing outside noises, or even you upstairs? I leave a radio on 24/7 in kitchen where my dogs sleep.
One method that has worked for puppy owners of mine is to go to him when he cries, take him out for a toilet, but apart from giving toilet command no interaction at all. Just stand around until he goes.
bring him back in but ignore him, put the kettle on, make a drink drink it, all the time ignoring him completely. He will eventually go off and lie down, after drinking your tea/coffee/cocoa quietly leave.
Repeat each time. the idea being that your presence is no big deal, no petting no playing, just boring, so night is for sleeping.
Other people put pup in a crate by their bed where they can speak to them, and even pet them through the bars for reassurance. they either have pup in bedroom permanently or gradually move him further away, hallway, landing etc