How long can I leave there's a big branch hanging in the tree before it becomes dangerous?

Now, if anything you use daily sits beneath it — vehicles, a doorway, a sidewalk, a play set, a dog run. Barricade the area before you do anything else, because the hold genuinely cannot be judged from the ground. And time runs against you rather than proving anything: the bark hinge dries out and loses grip, and every gust and freeze-thaw cycle degrades it further. A hanger that has 'held for a week' is measurably weaker than it was, not validated.