I agree with most of what you're saying, but the work will still be there the next day. I just dont see the reason to give more than agreed on, with the exception of emergencies of course.
So what is "agreed on"? There's no contract or anything in place, so is "agreed on" to always do the minimum amount of work required to not get fired? I'm sure many people enjoy going through life like that, it's just not for me.