I find the 20 minute on/5 minutes off Pomodoro cycle is great for getting me started into a problem. After 1 or 2 of these cycles I find I'm skipping the breaks

I find the 20 minute on/5 minutes off Pomodoro cycle is great for getting me started into a problem. After 1 or 2 of these cycles I find I'm skipping the breaks and sustaining focused work for longer.