There are a TON of reasons why the below won’t work for you, but if you’re in a white collar / strategic-ish type role (that isn’t IT for instance) where it’s not part of your job to be on call, then the below MAY work.

I’m a middle manager (Director). My advice to a lot of my friends in a ton of positions in different industries is this: Do not tell your boss / work something will be a certain way, but show them in actions. I.e. just don’t respond in a timely manner at 9pm (or whenever) and don’t give any excuses. “I have to (respond, log in, do this thing after hours)” - no you don’t. “I wasn’t free” is enough. Your company will get the picture. They will either understand they’re understaffed, or try to pressure you, but from my experience they’ll eventually just give in (if you’re good at what you so). Rarely will a middle manager actually attempt to replace someone (caveats of course) if you’re still pulling your weight during working hours.