In general, some airports will allow you to go through the security check-in much earlier while others may require you to arrive no earlier than 2-5 hours before the departing time. This is sometimes because the checked baggage counters and/or check-in gates are not open yet.

Whether you can check in five hours early depends largely on the specific airport's security policies and your airline's counter hours. At major international hubs like London Heathrow or Singapore Changi, check-in counters for international flights often open four to six hours before departure. However, at many domestic or smaller airports, airlines may not staff their counters until two to three hours before a flight. Additionally, many airport security checkpoints will not allow you to enter the terminal more than four hours before your scheduled departure to prevent overcrowding. If you are traveling with only carry-on luggage and have already checked in via a mobile app, you may have better luck entering the terminal early to enjoy a lounge, but if you have bags to drop, you are typically bound by the physical opening times of the airline's baggage drop desks.