[vkk8]

Depends on why those unproductive hours are unproductive. My hypothesis is that human brain is just incapable of doing the sort of forced, focused work that modern work requires for more than a small number of hours. I.e. the hours worked are just not randomly productive or unproductive (like your casino analogue suggests), but you spend the productive hours and then you move into less productive mode, which could just as well be skipped completely.

A related question is does the working capacity "charge" over the course of one evening + sleeping or does it require more time? If the answer is "more time", as I suspect from the fact that most productive days of the week usually are after the weekend, a good strategy indeed would be to just do all the work we can do (which is maybe 10-20 hours) in two days and then recharge for five days.