Yorkies, depending on size, need at least 10 weeks with their mom. She will teach her baby all kinds of socializing behavior that it will need as it grows up. Our moms frequently house break our puppies too (we have a dog door).
If your Yorkie is tiny, it might need to stay as long as 16 weeks.
I always suggest the the new "parents" come over for visits, even a couple times a week, to get acquainted with the puppy. Before we make the full transfer, we have 1/2 day visits at their new home. Then they come back and spend the night in the security of their mommy. Finally, we send fleece blankets that they have slept on with mom home when they make their final move. Of course, we also encourage visits after moving to their forever home.
I know they are so sweet -- that is why we raise them -- but let them become the best they can be before going out into the world.
Best wishes with your new baby.
Katelin