Hi Trilla maybe you coukd take Sundays off? Or maybe even the whole weekend? At the end of the day, you won't be awarded a PhD based on the number oh hours you put into it - its about producing quality work, and I know that I produce my best work when I my mind is fresh and I am not tired and stressed. I think you could set up a goal for everyday: explain a theoretical point, write 2-300 words, etc. Writing should not be such a torture!