How long can a fractured pinky finger knuckle/joint take to heal?

Many months. The crack in the bone itself heals in 6 weeks, but the swelling, stiffness and pain can last for many months. That's because it involves a delicate joint and because we can't help but use our fingers throughout the day and that keeps it aggravated. If your symptoms are still beyond what you'd expect, consider getting checked for a torn tendon.
About 6 wks. A fractured finger usually takes about 6 wks for the bone to heal. If the fracture involves the knuckle or joint, pain can persist because the joint has been injured. See an orthopedist for evaluation.