RAAFASA, with that attitude you'll get nowhere.
No, overtime is NOT optional. You are REQUIRED to work REASONABLE overtime. It's in the CA. The sticky is in the definition of "reasonable", and the definition ASA are expecting you to follow is theirs..people who never work overtime believe it is "reasonable" for those that do to come in whenever they are bloody well required, and anyone who says "no" in the knowledge that their refusal means closing airspace, well that's not just unreasonable, it's also "unprofessional" and "renegade".