It's really going to come down to which firm you're at and who your manager is. I'm at a smaller shop currently, and it's great. I basically work 8-5 most days, sometimes a little later if processes don't come up cleanly for market open at 5P (CME basically operates 23 hours a day with different trading sessions).
There are firms that are more like sweatshops. I spent roughly a decade at Citadel; when I started, average tenure was thought to be about 18 months. Hours were brutal, but it largely depended on your manager. I had one (he was fired 6 months after I started) that insisted on 80 hour weeks, ass in seat, no work from home, not even on the weekends. The kicker was, my team didn't even have the work at the time to justify all of us pulling 80 hour weeks. I also spent months at times pulling 100 hour weeks. That is, if you slept, it was at your desk (there were cots/sleeping bags available, but I never saw anyone bother). Maybe go home every 2nd or 3rd day for a change of clothes (you could shower at the office). Then, I had other managers where it was more 8-5. But, I was always on call 24/7, even while on vacation. That was the truly rough part. I would say on a whole, the reputation of working for Citadel is worse than it deserves, but it really matters who your manager is. That said, not sure I know anyone left at Citadel anymore other than Ken G. (I've been gone over a decade now).
My best advice when you're interviewing people, ask pointed questions about work-life balance. Avoid asking overly broad questions like "How's the work/life balance?". Instead prefer: "When was the last time you took a 2 or 3 week vacation?"
edit:
At my current role, I do sometimes work outside of 8-5 and on weekends, but its because I choose to, because I'm working on something interesting that excites me. I'm not expected to, and no one gives me a hard time if I don't.