Piece of string.
It really is dog specific, but start from day one with the basic stuff and it's only a few minutes a day. The dog should naturally indict it's more a case of you working out what it's telling you. Depending on several different thing's it might be indicting by six months or younger. But I believe in letting them be a pup and they can tag along on a hunt if they are under proper control.
And for want of better words, don't over train, especially early on.
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