when is it time to find new homes for Yen's kittens?

I would think so long as Yen's babies are 1) 10 to 12 weeks old, 2) are of good, healthy weight and size, 3) fully vaccinated with all three of the recommended kittens vaccines, 4) vet-checked and found to be free of any health issues or concerns, 5) spayed or neutered if you have a vet in your area that will perform early spay/neuter on pediatric kittens and 6) that they are well socialized and both eating and using the litter consistantly on their own, they would be fine going to their new homes.

Best to keep them till they are 10-12 weeks old. They need time to socialize with their brothers/sisters and learn stuff from their mother. Lots of times the mothers nurse 2-3 months even if the kits are weaned. So let them have as much time together.

Also during those 10 weeks, you can introduce them to people for handling and other animals (like dogs).

Although you can let them leave at 8 weeks - keeping them for another month will be more beneficial.

I agree with the others. 6-8 weeks is when pet stores tend to sell kittens, which is too early. At 10-12 weeks, the mother cat has taught the kittens all they need to know about grooming, litterbox manners and socialisation.