So I know this isn't practical for most people, but I've been able to choose how many hours I work on my day job for a while. My suggestion is: if you are a key employee or have any kind if sway, negotiate a lower or dynamic hour requirement in exchange for a pay cut. Once you start making over a certain amount you don't need more money, you need more time.

Wherever possible this will make you a happier person, not just give you time for your side project.

I actually think this will do a lot of good long term for the creative workplace as we learn to focus on efficiency and output instead of hours. It could open up more jobs too. So I know it's early and not often possible. But if it may be possible for you, I highly recommend doing it. If you do a good job you'll slowly make it possible for everyone.