4-6 months. I would recommend you wait 4-6 months after you stop breast feeding. That way the shape/size of the breasts have stabilized. It makes the results of the surgery much more predictable and enables the surgeon to more closely reach your expectations.
Typically 3 months. We normally say to wait 3 months after having a baby before having any cosmetic surgery procedure. The body needs time to heal and recover from giving birth.