When I worked in biglaw, one of the great questions was always: When can I go home?
It's never a clear answer, and many factors are involved, workload being the least important. Rather, the pertinent issues are: Where is your office located and what is its proximity to the elevator? What offices must you pass on your way to the elevator? Who else is still in the office? Who might you run into in the elevator? If you leave your office door open with the computer on, can you create the illusion that you are just stepping out for a cigarette?
I'm not doing this conundrum justice. It's a delicate dance.
Suffice it to say that in my first job, I would at times take the fire stairs five floors down to a different floor, so I could take an elevator in a different elevator bank.
For a true depiction of the complicated thought process that departing your biglaw office entails, check out this blog post I randomly came across today, entitled "Lawyers, Can You Go Home?". It features a flow chart that is so accurate, it's scary.