we often leave ours for 4 hours. (although we both usually work from home)
Occasionally we have left him for 6, but then we get a friend to come in an let him out for a wee.
twice he has been left for 8 hours, first time by accident (friend forgot to come over) he was fine. I know that, because when he isn't fine being left he finds things to chew, and takes items of ours to his bed.
BUT, he has had a 1.5 hour run before we leave him for 6 hours, and then is left with a Kong with peanut butter in, which he spends all day licking.
I think that your dog is too young.
If he can't get out for a wee, he will not be able to hold it for that long, and will be upset about weeing in the house.
He will be distressed, as it is not usual.
Surely someone could come round, let him out, spend half an hour with him and leave? Many of the dog walkers round here would do that if you don't wnat him to be walked?