My job is similar to solving math problems but in front of the computer screen. I'm starting to work 8 hours a day. Can you give me some suggestions to calm my mind and chill so I don't get burn out?

What I came up so far: Meditation, learning guitar or piano, meeting new people and doing some activity with them somehow.

Basically this is what I'm looking at: 9hrs sleep. 8hrs work. 2hrs self investment. 5hrs entertaintment.