How far in advance must a pilot file a flight plan for it to be valid?

A pilot must file a flight plan at least 30 minutes before takeoff for it to be considered valid. This timeframe allows air traffic control and relevant authorities to have sufficient time to process the flight plan and ensure that the necessary resources and clearances are in place for a safe flight. Filing too close to takeoff can result in delays or complications, as the information may not be adequately reviewed or acted upon in such a short time. It is crucial for pilots to adhere to this guideline to maintain safety and efficiency within the airspace system.