You need to get him back asap to the vets. The smell is the pus which is still full of bacteria. The blackness may mean the tissue has died and become gangrenous which means it may spread and cause blood poisoning.
This sounds as if it will need an operation to fully remove the dead area of skin, flush or remove the abscess and repair of the area that is damaged. I really hope it is soon enough to still be possible
Don't mess with honey on this wound till you have seen a vet
It is very sticky and the hamster will lick it and the wound may get made worse
Good luck at the vet but do get in as early as you can.