That's great. You should never take a senior position at a startup. Or, for that matter, probably a senior position at most any company. Which is fine. Different strokes for different folks. But some people prioritize career advancement over free time on the weekends.
Typically offsites (for me, as a senior level engineer) happen during the work week, not during a weekend. I feel that people are more productive and creative at offsites during regular work hours because they're not thinking about what they could be doing instead (like going on a camping trip with friends, for example).
I agree that my weekends are mine, and there needs to be a work/life balance no matter what position you are in.
Yes, all of my offsites have happened during the work week, as they should. The idea that senior engineers should ever be expected to work 12 days straight (5+2+5) is absurd. Yes, it's still a work day if it's an "offsite".
This seems like a pretty snarky comment. I've worked with some incredible senior people who had nothing to do with the company out of hours.
I think equating hours spent with career advancement is a mistake. In my more junior days (in which I include senior roles) I gave far more hours to my job than I should have. In the scheme of things that was a mistake and I could have advanced my career much more by approaching it differently.
Your comment feels like something that might have made sense decades ago, but is not necessarily great advice these days.