After 9/11 passengers on flights to Washington’s National airport were required to remain seated for the last 30 minutes of their trip, and for the first 30 minutes on any flight departing the airport.
Dubbed by frequent flyers the “no pee rule” it was meant to immediately identify anyone that might be trying to take over the aircraft when it was close enough that it could hit the White House, U.S. Capitol or other high value target. More than 30 minutes out, presumably, the government thought it would be able to shoot down the plane.