Being self employed working from home (coding), I recently started to do some timetracking to see how I spend my work. I used pomodoro technique with 25 minute slots and 5 min breaks in between. I set up an initial goal of doind 10 per day or about 5 hours, sounds very modest to me! Also, I set a rule that I have to stop working when I felt mentally drained, you know when you just feel sluggish at the end of a normal working day.

The thing was I struggled very hard to reach 10 and found a nice balance at around 8 slots of focused work per day (4 hours, ncluding coding and administrative tasks). So a 25 hour work week suggested in the article sounds reasonable to me.