The best time to book Christmas flights can vary depending on several factors, such as your destination, the airline you're flying with, and your travel budget. However, generally speaking, it's recommended to book flights as early as possible to secure the best deals and ensure you get the flights you want. For domestic flights, booking 2-3 months in advance can be a good rule of thumb. For international flights, it's best to book at least 6-8 months in advance. Additionally, it's always a good idea to keep an eye on flight prices and to book on weekdays when prices tend to be lower.