Sunday was just an example. Nobody is stopped from working if they're movitated to do so, but we generally discourage each other from working overtime unnecessarily. I personally work 32-hour weeks regularly and still contribute meaningfully.
And then, I go backpacking or bike-riding or something that tends to be demanding physically and relaxing mentally—I find it helps me keep a healthy balance. I know there are plenty of people that don't crave that reprieve though, and that's totally okay as well.
There's weekends where I'm working on a particularly interesting problem where I'll work through the weekend because I want to. The big difference is the extrinsic pressure is missing. Nobody has to.