Author here. I don't factor in lunch (so take away 30-60 min). Also, the 19:30 stop is there as a hard stop. Sometimes I feel drained at 17:30 or 18:00 after a very productive day. In that case, I'm happy to wrap up the day.

That was also my first thought, I feel 10 hours (or even 9 hours) is extremely long. Being laser focused for 9 hours is extremely hard to do on the long run. As others said, you need to find your own schedule but don't aim for 10 hours first thing, go slow

Different people have different ideal workloads at different times in their life. People need to figure out their own healthy velocity.