For each season (the author suggests to split this 3 times per year, or one could do it quarterly) to choose a hobby to focus on on your leisure time, such that it is also measurable and has an intent/goal. An example mentioned is playing guitar, especially the A-sides of a Beatles album, and by the end of some time there, to organize some concert to play.
It is emphasized to do this seasonally, but obvi this requires to organize your weekly schedule to accomplish these leisure goals.
It is important, since doing nothing is overrated (his words). By actively seeking out high-quality leisure activities and scheduling them, you are more likely to keep
He attaches this to the idea of eudamonia by Aristotle.
Reminds me of this video