I’m the same way, Jeanne. If you subscribe to Skye Warren’s author newsletter, she’s talked about our brains losing their effectiveness after about four hours of work. I’ve read studies about people who work eight hour days, and how the amount of actual work time is significantly lower than eight. Our culture has become one of working endless hours, but we quickly lose efficiency and it really doesn’t make sense to do it.
I’m a fan of The Chunky Method, too. That’s how I work. I like to write for 30-60 minutes, then take a break and do something else, and go back to writing when I’ve given my brain a chance to rest.