When coming home for lunch, make sure pup eats and make sure pup eats before you leave in the morning. Really any exception to that could put him/her in a bad situation.
If possible, come home on breaks or have somebody else check in.
Yorkies are extremely vulnerable to hypoglycemia at this age.
I got Ellie at just less than eight weeks. Didn't know any better at the time and I don't think her breeder did either. I love her to pieces, but I also have learned a valuable lesson. That is, this is far from the optimal time to take a Yorkie home.
And just because someone works full time does not mean that they shouldn't be able to have a puppy! Wonderful for everyone that has the ability to stay home, but for only stay at home owners to be considered good puppy candidates really isn't fair, imo. As long as the pup is taken care of, it's just fine.
You may want to consider a playmate for your pup after awhile.