The 45-minute rule means airlines can release your seat if you haven’t checked in or reached the gate by at least 45 minutes before departure. Many U.S. airlines use this cutoff to finalize boarding lists, assign seats to standby passengers, and avoid delays. It’s especially important for busy travel periods when security lines may be long. TSA recommends arriving 2 hours before domestic travel to avoid missing this cutoff.
Official guidance on airport timing:
https://www.tsa.gov/travel/security-screening
