I am a firm believer that the brain has finite resources. It is fundamentally no different than a muscle, in that, the muscle has resources at its disposal, and using those resources causes them to deplete faster than they can recover. This means, that at best, you can optimize how you use your brain, similar to how you can optimize how you use your muscles. You can train, to get "more" out of your brain, similar to muscles. But at the end of the day, there is only so much your brain can do. I have found, through fairly good time keeping, that I can do ~6 hours of deep work in a 9 hour period. Maybe 7 in a 12 hour period. This is the amount that puts me at the edge of burnout, and requires no other commitments in my life. 4-5hours in a 7.5 hour day is sustainable. Others may be able to do more, or less than this, but many people are fooling themselves if they think they are doing good work that is also deep for more than this, for more than say 4 weeks at a time.

That said, if you can find ways to use very different parts of your brain... well, then you can squeeze out more performance. In the same way that in the gym, if you find exercises that isolate different muscle groups, you can squeeze more sets in throughout your workout.

I have seen this with people who can produce a lot of output, they tend to not do the same thing all day, but find ways to work on unrelated projects. So, I'm not terribly surprised that you have an urge to code now that your brain is focused on non code related things for a large part of your day.