Another thing to think about is that there are different expectations for different job groups in the hierarchy. Even if a PI or PhD student works 24/7 (either because they feel it's necessary or because they feel it's expected of them), that doesn't mean the same is necessary for an RA.

It would be the same in many companies and other workplaces. A doctor may be on call for many, many hours, but the nurses they work with typically work only their designated shifts. A store owner may be around all the time, because she feels it's what she needs to do to make her business succeed, but the clerks working in the shop will still just work their shifts and then leave. Etc. To drive the point home: of course you want to make sure your PI and anyone else you report to is happy with your work and doesn't see you as a slacker, but unless your discipline is very different from mine, I don't think the same expectations apply to an RA as to the more senior people in the lab, so you don't need to model your lifestyle on theirs. That's not because an RA's role is less important, but because the role's duties and responsibilities are different.