That's actually close to a regular working day. 4-5h of core work, 2h of correspondence (e. g. Zoom meetings, bullshit emails), 1h of various breaks, e. g. lunch. Sounds perfectly reasonable to me.
If one of the best speculative fiction authors to live only needs 5 hours of work a day to create The Left Hand of Darkness and the Earthsea series, then maybe it's something worth exploring.
Most of us work 8 hours a day and probably produce nothing "valuable" except shareholder profits so...
For most of those 8 hours, we are not productive to begin with and just procrastinate over small tasks, because it's not humanly possible to be hyperfocused for 8 hours straight.