While each airport will have its own procedures, security generally opens two to three hours before the first departure of the day, and remains open until the last passenger has gone through.

For security and logistics reasons, most airports limit terminal access to 4 to 6 hours before your flight. At many international hubs, you can enter the public "landside" areas at any time, but you cannot clear security and enter the "airside" (gate area) until your airline's check-in counter opens, which is typically 3 hours before departure. Some high-tech airports like Singapore Changi or those in India have strict rules where security won't let you through the main doors until exactly 4 hours (domestic) or 6 hours (international) before your scheduled take-off. If you have already checked in online and have no bags, you might be able to enter the gate area earlier if the airport uses a centralized security system, but you'll still be limited by "same-day" rules. Arriving too early—such as the night before—is often not permitted unless the airport has an on-site transit hotel, as most security checkpoints close overnight and won't allow passengers to "camp" in the gate area for extended periods.