There have been workplace studies dating back over a century that show worker productivity peaks at about 40 hours a week. Productivity slows after that, and even goes negative.
I saw this when I worked in consulting and there was pressure to bill lots of hours, so lots of people worked late or on the weekends. But I quickly found out that if you want something done quickly and accurately, you give it to the person who leaves at 5:00 every night and doesn’t come in on the weekends.
In short, I don’t think Jamie Dimon is accomplishing squat by being in the office seven days a week, other than to wave the flag about how hard he works.