If you mean Pomodoros, then it doesn't count - the whole idea of "Pomodoro break" is to be short and spent in such a way as to not really break you out of focus.
If you can just sit down at random times and immediately code for 20 minutes with full focus, please tell us your secret. It sounds like a superhuman skill.
I do the same thing, 30 minute stints, 3-5 minute breaks. Occasionally if I'm really rolling I'll just keep going but I generally make sure to stop for breaks.
The key is to do things that won't get you mentally distracted, has a good stopping point, and lets you mentally rest.
Good breaks:
- I walk around the building
- Watch a short comedy youtube video
- Scroll through memes/comics
- Read blog posts, usually ones that aren't too detail-oriented and with good stopping points (Coding Horror is a good example)
- Listen to an instrumental music song (no lyrics), close my eyes, maybe get some fresh air.
Bad breaks:
- Start a long email
- Other projects.
- Anything mentally taxing or stressful (don't pay bills on break, don't try to figure out what you'll have for dinner)
- Read an exciting book that you don't want to put down
Doing this helps me stay focused all day. Over an 8 hour shift I take breaks for approx 48-80 minutes (plus lunch), so at most a little over an hour is wasted--versus burning out after just a few hours, writing bad code that I then spend the next day cleaning up.
This further translates into me being able to work some more on some side projects when I get home without getting burnt out--and not always programming, but other mental work like writing, art, meal planning, etc.
If you can just sit down at random times and immediately code for 20 minutes with full focus, please tell us your secret. It sounds like a superhuman skill.