Yes, it's just norms. 15 years ago, I worked for a small startup. For a good 8 or 9 months, we were working 6 and sometimes 7 days a week. We weren't contractually required to, but everyone "wanted" to. I use scare quotes there, but I think a lot of people (myself included, for part of it), really did want to.

But ultimately the unsaid thing was: you either work 6/7 days a week, or you get marginalized or fired. And it's not like we weren't putting in the hours on the weekdays; most of us were working 12-hour days, or more. (And wow, we got to drop down to 8-10 on the weekends! So generous!)

Dumb. I'll never do something like that again. Not worth it, and certainly not for someone else's company.