If a universal basic income started today with the stipulation that you had to put 40 hrs/wk towards making the world a better place or solving societal problems, how would you spend your time?

I'm with you on the 40% thing. If I didn't need to put in 40hrs to get my health insurance, I would absolutely work on several smaller tasks instead of 1 big job, just to avoid the burnout that comes with doing the same thing for those long stretches of time. It also gives us context and allows us to make connections that we may not otherwise make.