First, I am not trying to make anyone upset. I have read that the best time for human bonding with the puppy is from 8-12 Weeks. Also, they learn things best starting at 7 Weeks and are usually weened by 5-6 Weeks. I have read some post before but the only argument I can recall is that they are too small.
Some dams wean and instruct their pups earlier, some later.
If a pup is going to exhibit signs of ailment or infirmity - it will invariably be before the twelve week mark, and not necessarily before the eight week age. As a breeder we'd rather deliver a healthy pup with an ultimate opportunity to thrive in its new family environment - and, as an owner, you should want the same. Additionally, a toy breed pup at eight weeks is injured so very easily - a fall from the bed or sofa, dropped from unsuspecting arms, caught in a closing door as it attempts to follow you into a room. An eight week old pup is better off in its breeder's house, where it has obviously thrived in a safe and secure environment to reach this age, than to make a risky transition into a new environment.