
Now that the "reply" box has appeared!!:p....
I have always started the "recall" training as soon as I can - with a home-bred pup, from about 4 weeks, or with a "bought-in" pup, about 3 hours after we get home (having allowed time for some exploration, food and a nap)! I crouch down low, and call "Puppy come, come, come" in a high, happy voice, and puppy invariably comes running. I call the puppy to come every time I feed it (lots of meals = lots of training opportunities). I only call when there's a high chance that the pup will come - each ignored summons teaches a pup that coming when called doesn't matter.
By the time the pup's injections have taken effect and he can go out, the basics of recall are well established, and only need practice in all the other possible situations.