Hi and congrats on getting your new baby boy
The YTCA recommends that they stay with their mom thru 12 weeks. At 8 weeks, the small dogs like yorkies can get hypoglycemia when they are young. Staying with mom is important. In addition, during that 4 week span the puppies learn behaviors from mom and siblings.
If she says 7 weeks due to bonding, she's blowing smoke up your *ss. Sorry, but that is ludicrous. I don't even think it's legal to take a pup from it's mom before 8 weeks (no matter the breed).
If you want what's best for your new baby, ask your breeder if the pup can stay thru 12 weeks (even if that means paying in full at the 8 week mark...)
Good luck and it's great that you are asking and researching!