A side project is creative while work is reductive (not necessarily a bad thing!)

Side project is graffiti art on your shed wall, day job is 3 coats gloss white on the ceilings. That needs to be finished by Friday.

I have some side project ideas but need the time! Mainly these would be contributing to OSS databases to get (any!) knowledge of systems proprogramming. Node.js or Go preferred due to familiarity.

Great metaphor but I feel like my day job is graffiti style crap code that just barely passes QA while all of my side project code is the good good 3 coats of SW superpaint

Graffiti can be as beautiful or messy as you want! You can put any amount of effort in to the craft