Anyway, work that requires focus should have natural rhythms: There's things that need to stay in my head, and if I get interrupted it's very hard to find my place. So I work without stop (except to pee) while these things are in my head, and I take a break once I finish enough that I can "forget" what's in my head.
It's something you'll understand if you've ever written complicated programs, or had to do something that requires intense concentration.
For example: I had to tweak a server-side Blazor application to deny access in a certain situation. Last Friday I did it in the UI, but that's not a good solution because there's ways to accidentally bypass the UI. The right way to deny access is in the Middleware, but I didn't have a lot of experience working with ASP Middleware. Thus, I couldn't start working with the Middleware in the last few minutes of the day (too much to learn).
I spent about 90 minutes this morning learning how to hook into ASP's middleware so I could deny access to the application. Once I learned how to do that, I ate lunch. After lunch, I closed all the browser windows that had the documentation for Middleware and wrote the error page. Now that I opened the PR, I'm taking a break on Hacker News.
Trying to fit that into a timer is impossible: If the timer went off while I was trying to figure out how to work with the Middleware, I'd have to re-read a lot of the stuff to get back into the puzzle.