As social animals who will eventually face the loss of every friend we've ever made, cultivating both a good network of friends and a kind of internal resilience is probably the best way one could choose to invest their time.
There are many very questionable ways to invest this finite/precious time, and most of us don't think twice about how much of it we squander (e.g. spending time online). There is a small category of things to focus on that is almost universally worth the effort: sleep, diet, exercise, social connection. Focusing on these things also tends to help establish that inner strength.
The difference is very stark. I probably made 1-2 good friends in the _10 years_ after college, compared to 30+ friends in the 10 years prior to that. Luckily, I managed to keep most friends from before starting work.
Full time work is an absolute black hole of time and relationships.
People who don't have good networks _before_ they start full time work are absolutely boned and I don't think there's an easy solution.
Improve your friendship network and improve resilience.