Here you go... from the breed club website.
Yorkshire Terrier Club of America (Awards)
And...a show breeders website.
VanGogh Yorkshires
At what age should the pup be when you bring it home? No one should bring a Yorkie pup home younger than 12 weeks of age. Why? Yorkies can easily get hypoglycemia - low blood sugar, brought on by stress. This stress can be as simple as moving to their new home if younger than 12 weeks of age. Think about when you have made a move in your life. Yes, it is very stressful. Research has proven that a move is the second highest stress in ones life other than a death in the family. Any breeder that tells you that their vet said it was okay for them to leave to their new home younger than 12 weeks, either does not know yorkies well or they do not care and want to not have to clean up potty from a puppy. Puppies make a bigger mess when they are from 8 weeks and up. When you have a litter - that can be a big mess and a lot of work. This is the main reason unreputable breeders want their pups to leave early. So do not be fooled.