Their can be two sides to this, if the breeder wants a show pup out of the litter they tend to rehome later as they want to make sure they are getting the best pup. As stated before the age to get a puppy used to be 6 weeks Most people rehome at 8 weeks or as near as possible to that date, most mums loose interest in their pups quite early after weaning, just checking they are okay so rehoming earlier will make no difference to the bitch. Personally I think the younger the better, you can get them vaccinated, out and sociallied that much earlier, which I consider much more important than a few extra days with mum . Over the years we have had 2 cross breed pups at 5 week, which was really too young, but they both turned out fine.