Whether you can check in 6 hours before a flight depends on the airport's security rules and the airline's counter hours. At major international hubs like Delhi Airport (DEL), terminal access is officially permitted up to 6 hours before departure for international flights, allowing you to enter the building, check your bags, and proceed through security early. However, many airlines in Europe and the U.S. do not open their physical check-in counters until 2 to 4 hours before a flight. If you have only carry-on luggage and have performed a "web check-in," you can often enter the secure area as soon as the TSA or security checkpoints open for the day. For those with checked bags, arriving 6 hours early may result in a long wait in the "public" side of the terminal until an agent arrives. Some premium airlines and specific airports (like Singapore Changi) offer "Early Check-In" lounges where you can drop bags many hours in advance, but for a standard economy traveler, 3 to 4 hours is generally the functional limit for bag drop-off.