How long before seperate puppy from mother dog

I think that it really depends on the development of the puppy. When the mother starts weaning the puppies, then it is time to start supplementing them with soft food, and gradually they are eaned from just nursing, and more into eating puppy food. Once the mother has weaned the pups completely and they are able to eat as much food as they need to grow and be healthy, then they are ready to be taken away from the mother and re-homed.
It is good to handle the pups from the time they are born, so that they are used to being around people, although it needs to be done very gently since they are so young. This helps them to make the adjustment when they are given away or sold, if they are used to being held and petted,and look forward to human attention.
Since puppies are pack animals, taking them away from the rest of the litter is going to cause the puppy to be lonely and cry. Giving them a small stuffed animal (about the same size as they are) will give them "another puppy" to cuddle up to when they are sleeping. Chipper had a little Squirrel when he was a puppy, and he loved that squirrel, and always slept next to it when he was in his baby bed.