I seem to recall that what was more important than the amount of time spent studying, was that the students were engaging in deliberate practice; they were putting in focused work intended to extend the boundaries of their skills. I think the analogy here would be that three hours of focused work (door closed, phone turned off, no checking email, no interruptions unless the building is on fire or someone is dying) would produce more, better quality results than 8 (or more) hours of work broken up by dozens of interruptions.

I still get distractions and end up doing filler non technical work during those first 3 high-speed hours, but I try to go at a pace as if the world is coming to an end and I need to give my work its full and qualified attention that it deserves...just like I use too when taking tests during my university days

We have a gym at work and i have felt an amazing refresh when I go gor a midday workout, but sadly it looks bad to leave work to workout during normal office hours, and the gym is too packed during lunch for my taste