We generally don't want you to work overtime. We need your creativity and energy, and they require rest: on a daily, weekly, monthly, and annual basis.
On rare occasions — reaching a publicly committed deadline or solving a production emergency — it might be necessary to work longer than usual. We expect you to do what is necessary and then take extra rest time at your judgement.
Pet projects and other extra work activities are fine, provided that you are doing them for fun.
A results-only work environment requires trust and full commitment, so it's not ok to work overtime on other commercial projects or do side jobs, unless explicitly agreed upon.