In my view, contribution to open source falls under hobbies, so the time comes from the leisure time. I agree that if someone takes that from sleep time instea

In my view, contribution to open source falls under hobbies, so the time comes from the leisure time. I agree that if someone takes that from sleep time instead, they're harming themselves, but this still is nothing the employer should (be allowed to) care about. If the employee underperforms at work, the employee gets a warning, and it is up to the employee to review his or her time management, being a responsible adult that they are.