Be a grownup and assert that your work is at work, and work ends when you leave the office. Unless you are on call, turn off your email and work phone. Stop being conned into staying at the office for "free" dinner, ping pong, "teambuilding", or whatever bullshit is being peddled by your employer.
Or they can hire more people.
In some countries, it's extremely unusual to perform overtime. If a startup has 10 employees and they each do an hour of overtime a week - they're effectively denying another worker a job.
Yes, it's a bit "mythical man month" - but if there's too much work to go around, your employer needs to hire more people.
Obviously, ideally none of this would be necessary. But alas...
Reasonable, sure. But is it realistic when we have things like this https://news.ycombinator.com/item?id=11430596 ?