Honestly this depends on so many things.
1) your office
2) your projects - meaning your clients
3) your team - meaning your direct managers and partners
4) you - your ability to do the work quickly and communicate honestly to your managers and team how much time you need for which tasks
5) honestly prioritizing: being prepared (and this takes some confidence that takes time to build) to have a prioritization converasation with your manager - meaning you assert you have time for 3 tasks and therfore the 4th one will have to wait until next week. This isn't easy at first but is almost the most imporatnt thing you can do to save your work/life balance.
Your firm question: Honestly I don't think it depends on the firm. I've seen so many realities in McK worldwide in the US east coast vs. US west coast, Australia, UK, Netherlands etc.
Lastly, if helpful at all:
- there have been months when I worked on average until 3am.
- there have been months when I worked until 8pm.
- there have been months when my average was until midnight.
- I only worked on a weekend twice! And each time for 1-2 hours.