I find that people who eat, breathe, sleep advertising do very well and thrive in 4As agency. So that means you rarely have a life outside of work as you are pouring everything, your passion, even your time even outside of work, into the current project. I mean, you can still get away with working the 9-6 and have a life, but it will still look like you're not doing enough to contribute to the project.

But honestly if you have the chance, you should do it while you are young and have the energy. The experience you'll get is is really quite something else, and you could always take that experience to a smaller agency with more work-life balance.