How long?

I'm in line with Judge Peels position.
Also, if you want a pack of good dogs, you will probably go through several dogs to get what you want. If you start with pups, you will have a lot more time invested in the dog in order to see what it's going to be rather than buying an adult dog. To get a good set of dogs, you have to cull the ones that don't make the grade. Training and patience is also importent. You get know where if you cull good dogs because you your lack of ability to read your dogs, analyze things CORRECTLY, and so on.
I personally have a tendency to start with pups from best bred to best from dogs that hunt the way I prefer to hunt. I have a long time invested in a dog that might not suit me though.