Hate to break it to ya boys but Investment Banking/Big 4 Accounting/Top Tier Law is almost certain to kill any fitness you have and I'd be very surprised to see any time in your schedule for getting it back.
I've worked Mid Tier law and even there 60+ hour weeks are the norm (8-10 billable hours a day), I have a very good friend who spent 3 years as an Investment Banker and he ended up working far more than that (and usually at odd hours too - apparently IB offices like to keep in sync with market timings outside Aus?).
If however you are a machine who can manage a gym session after 15 hours at the office (I've met some people who can - which challenges the certainty of my initial assessment doesn't it?
) I recommend having a read of
Dan John's article on barbell complexes. Fast and efficient ways of getting a very good cardio workout while disrupting homeostasis enough to increase size/strength (well up to a point). You'll never be the strongest guy in the gym training like that but it might be a good compromise for the busy professional.
As an aside, well done Jim on securing such a competitive job in such competitive times - kudos.
Oli - my advice as a recent law grad (now cruising as a government lawyer) is not to buy too much into the law school heirarchy what says Top Tier law is the ducks nuts and everything else is not worth doing. Top Tier will work you to the bone and will not pay as well as everyone thinks, and if ever you want to be anything but a one dimensional lawyer (e.g. a property lawyer or an insurance lawyer) you're in trouble (BigLaw is not about diversity of expertise)
With that said though if you can stick it out long enough and you're a white male (I presume you're OK there?) you have a shot at making partner and then you'll actually be making the sort of money everyone thought you were from the outset.
Cynical rant over