That’s FOUR days.
If the balloon was 200 ft tall like reported, there’s no way it wasn’t detected until Jan 28th.
U.S. officials first detected the balloon and its payload on January 28 when it entered U.S. airspace near the Aleutian Islands.
Ya never know when the object was first logged. This is the information released.
The balloon itself was most like invisible to radar. Radar can’t see anything that it can pass through without reflections.