I find working a lot of hours can lead to confusing activity with results. When you're gaining experience you don't know what to focus on so you spend your time focusing on things that don't matter in the end. As you get wiser, you learn to focus on what matters more, and have the choice of doing it more, or not.
One other very big caveat is this type of a conversation with me when I was 20 would have been tougher because I had much less of a clue of what else was out in the world that I couldn't live without and wanted to have as part of my life. It's also what allows young people to give up their 20's pursing startups that have little to no chance in hell of setting them up to chase their interests for the rest of their life.
It's also why I very much agree with PG's advice to simply solve actual problems as a student, as the closer you are to solving problems, the closer you're to value that can carry you forward into the next thing you work on.
Invariably, many 20-somethings don't know much about the world, or what's in it. The more time spent behind a keyboard the more once can be left behind the eight ball in becoming well rounded enough to interface with the problems that are out in the world that need solving.
Life hasn't been binary for me so far, there's no specific generalization available to follow. Instead of focusing on one thing for 60 hours a week, I've found that paying attention to make sure I'm growing and having experiences that are helping me grow in a meaningful, satisfying, fulfilling, and lasting way was enough to kind of get the hang of.
Getting caught up in the echo chamber of doing what others doing got me what most others got -- not much that I valued for those hours, until I changed it up.