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This is a difficult question to answer as the fares can change daily as people from all over the world book, change and cancel their travel arrangements.
However, the general rule is, the longer you leave it until you book your flights, the less likely you can pick up a cheap ticket.
This is particularly true of what we call "peak travel periods" such as public holidays, school holidays, weekends etc. For these travel periods, the cheap seats usually sell out fast and it is better to book as early as you can.
However, the airlines can release sales at any time and maybe a lower fare does become available but this would be a risk you would have to take.