There is at least something at risk if you work on something people start to use because people start to have expectations about it continuing to be useful. They want bugs fixed, new features, the project not to die, etc. One risk is you make a lot of people upset. Another risk is you're viewed as irresponsible for starting something and leaving it half-finished.

So if you're "just" volunteering and don't deliver you possibly risk as much as your career.

The time constraints you're under are the time constraints of your free time in your life.