Not sure if it applies to "pigtailing" but here goes: Good for general purpose anyway.
at least 6" of free conductor measured from the point in the box where it emerges from it's raceway or cable sheath, shall be left at each outlet, junction, and switch point for splices or connection of luminaires or devices.
Where the opening to an outlet, junction, or switch point is less than 8" i any dimension, each conductor shall be long enough to extend at least 3" outside the opening.
Gigs, I was not asking how to wire a pigtail, I was asking how long it should be. I figured if the NEC gives you requirements (minimum) on just about everything else regarding distances, lengths and so on that there might be a required lenght for a pigtail. Thanks for your time.