This timer runs 50 minutes of focus followed by a 10-minute break, with a 20-minute long break after every fourth block. It is often called the double Pomodoro: the same structure, twice the depth.
It suits work with a real warm-up cost — writing, programming, analysis — where a 25-minute block ends right as you have finally loaded the problem into your head.
When 50/10 beats 25/5
Every block starts with a few minutes of re-orientation: remembering where you were, rebuilding context, getting back into the material. In a 25-minute block that warm-up is a big share of the time. In a 50-minute block it is a small one.
The trade-off is that you have to be able to hold attention for the full 50. If you consistently drift at minute 30, go back to 25 for a while — that is not a step backwards, it is the right size.
It also fits the clock
Fifty plus ten is an hour. That makes the rhythm easy to plan around: one block per hour, starting on the hour, with the break landing at ten to. Many people find that predictability alone makes the day easier to protect.