oh yes forced office hours are so horrible.
i felt the exact same way when i was working for a local korean game developer. the best time for writing code was early morning when nobody was around! (and i used that time to write my own shit instead of working because i was underpaid)
sometimes i concentrate for hours and hours but i also like to take some big breaks every now and then :)
if you can figure something out to go indie and still make a living it's the best thing in the world! 👍