Welcome to YT so glad you found us.
Your little guy is very young so I could understand why you would be worried about leaving him alone while you are working such long hours. He is too young to be taken to Doggy Daycare for that is not even an option for you until he is fully vaccinated at about 16 weeks. Could you possibly pay a neighbor to come and check on him during the day? Do both you and your husband leave at the same time or is there an overlap so he is not left quite so long.
Puppies will sleep a lot they are just like babies and being that he is only 8 weeks old he is pretty much a newborn so it is to be expected. You are feeding him a decent food so that is good.
He should go to the vet in the next few days to be examined to ensure that he is healthy too. As others has said it is very important that he eats and drinks for that he does not get hypoglycemic which is very dangerous.
Really is does not matter if he came from a pet shop or from a breeder at this point, it is just good that you have found YT so that you can have help if you need it.
Do you have him in a crate or an Xpen? How do you plan on containing him while you are at work? An Xpen is wonderful it allows them to move around and also be contained for their safety.