This professor at University California Merced advises to take the weekends off, along with some other pretty canned advice, like take a walk without your cell phone and meditate. The argument is that working more than 40 hours a week can be counter productive. https://chroniclevitae.com/news/766-take-the-weekends-off
I agree. I take one full day off, Saturday, and my long term goal (like when I have a real job) is to take weekends off completely. But you have develop the work habits, time management, priorities in order to get to the point where taking weekends off doesn’t just mean sacrificing a bunch of work time. More recently, I have made my goal to work 7 days per week. I already don’t work very much, usually 30 hours per week or less. Given the life circumstance of having a young kid, you generally have less work time in a given day, week, month, and you have totally unpredictable interruptions. So I make up for it by working on weekends. And I feel like for this point in dissertation writing the most important thing is to keep the momentum going at all costs, and the best way for me to do that is work a little bit EVERY day.
There is also the issue of quality. I work 25-30 hours a week, but that is active working time. I don’t time breaks, commuting to campus, eating, internet surfing, etc. I do count meetings and any event, seminar. If I hit that timer, I am sitting in my chair just working on whatever task I have set myself to. I feel like this gives me more freedom to really mentally break form my work–when I am not working, I am NOT working, and generally not thinking about working or feeling guilty about not working.
(Side note: The two most useless emotions related to dissertation writing are GUILT and DOUBT).
In conclusion, I agree that there is a tipping point at which working is just counter productive in terms of burning you out and poor quality, and that I need designated, sometimes extended, time off in order to stay focused and productive.