I don't know, I raised Babs and Jenna together, and then brought in Rushie when they were 5 months old, and when, and then seven months later had Heidi, Whit, and Tori. And I did that, titled them all and was working full time. It really depends on the dogs and your expectations. I think it is a little easier if you are not overwhelming the dog with tons of training, socialization, etc. I take my time in training them and am not expecting miracles by the time they are 6 months old.
I can usually get their CGC and RN by about 1 year, and by the time they are two, they are pretty much where I want them to be.
Jenna, RN CGC & Babs, CD RA CGC HIC
Heidi, RA CGC
SG3 Odessa, SchH1, Kkl1, AD
Ninja, RN CGC & Milla, RN CGC
Joy, Star Puppy, RN CGC
Dolly CGC & Bear CGC