I keep seeing endless studying habits writeups showing people studying for 12-15hrs straight and I don't understand how anyone does it.

I have been tracking my working time lately with a timer, and I am pretty strict on what I classify as getting work done vs not_work but pic related is the typical day for me. Nomatter HOW much I try to get my working hours above 8-9 hours, I can never seem to. The other stuff in my day just seems to naturally fill up the other ~8hrs regardless of what I do. How do I get this number up and work 12+ hours in a given stretch? This 9hour is because I didn't shower or change my clothes that day, that is why there is an extra hour, my normal day is always 8 hours or less of actual work.