...or you could do an Albert Einstein, who worked as a patent officer. He could finish the job in 2 hours and spend the next 6 hours working on his theories.
Yes you just need a job where (a) you can do it in fewer hours and (b) you can do your other thing without being noticed and (c) your other thing is in the public domain / learning based as you don't want to give the IP to your employer and (d) there is no scrutiny about how you spent your time via Jira reports etc. and (e) it is an environment where you can concentrate on the other thing. I think AE's job was such a job but harder to find nowadays but I think government jobs are more likely to have these qualities.