The Pomodoro Technique recommends breaking down work into intervals of 25 minutes in length, separated by short breaks normally 5 minutes.

Is the number 25 magic? Is there any research that says that a 25 minute focused session is the optimum?

Not as far as I know. I’m even pretty sure that it’s impossible to find a worldwide optimum session time. It depends on who you are. It depends on your type of activities. It depends on who you work with and what responsibilities you have to them. It depends on if you’re tired, or if you’re in good spirits on a particular day.

Short iterations are more often completed. If you are constantly interrupted, it indicates that you should shorten your Pomodoro length. It’s easier to stay focused all the way through when you have smaller iterations.

If the iterations are longer, there are fewer breaks, but on the other hand, the breaks tend to be longer as well.

Every Pomodoro Technique practitioner has the option to experiment and find her own optimum. But I urge you to start with 25 minutes and stick to the same length for at least two weeks. Changing the length all the time destroys your rhythm.

-- Pomodoro Technique Illustrated; ch. 5 Adapt; sec. Length of Pomodoro