The advice in this article is very on-point. I would add that a creative project can also be done at your current job. If you have the freedom to take on new responsibilities, it will be generally seen as a positive (who doesn't like employees that work late and on the weekend?). You might even get a promotion. How that compares to doing something on the side is up to you, but I would recommend not seeing work as just work, but a place where you can experiment in an existing enterprise.