Totally agree with Carrollfamilylabs. Wait til 8 weeks and ask your friend to actually keep the pups until they are all 8 weeks old. By that age they develop their social skills and have learned how to correctly interact with their littermates. Pups that are separated from their mothers / littermates at an early age usually don´t develop the social skills and can become dog aggressive or shy when they grow up.
What you can do if your friend allows, is to start visiting the pups frequently so they will identify you as a friend and will have an easier start once they are ready to go with you.