Are you literally scheduling everything you do? Are you sleeping less than 6 hours? Obviously, there's probably 2 hours per day in small intervals where I'm not maximizing my day.
Because of this, I recently picked up guitar, and this is nice for the random periods I'm free, because I feel like picking it up 4 or 5 times a day for 5-10 minutes still allows me to make a lot of progress, be creative, and learn a lot about (and appreciate) music.
Chess is also something you could do this with, but I feel like at that time scale it would be harder and less rewarding, and this is still about 1/4th of the two hours mentioned.
Edit:
I probably spend 30 minutes on HN per day, which is mostly a waste. But this is also in small intervals.
The downside is of course that sometimes the other important things are hard to maintain. But this is how you do it.
Admittedly, level of challenge in games can vary tremendously. I always like to have one on rotation that is difficult.