How many hours a day you consider a good day of work ?

Genesis C.
If you are talking about actually focused time (as with deep work), then I think 5-6 hours is a very good day. In my experience, the 8-hour day includes a lot of time for distraction, answering random questions, etc. I am also personally quite worn out after 5-6 hours of deep work and it can take 8-10 hours to get that time in.