The eminently sensible Usha Rodrigues offers up this advice for young faculty trying to find a work/life balance:
I had a mentor give me excellent advice my first year:
Just say no.
At least, your default answer should be "no." To my chagrin, I realized something at the end of my first year of teaching: This job has infinite demands. There are 3 elements to it: teaching, scholarship, and service. You could devote every waking moment to your teaching, and still have more you could do. Ditto for service. Ditto to the nth degree for scholarship: always another talk you could attend, an article you could read. But you can't do those things and write. At least, I can't. You have to get used to always feeling like there's more you can do. You'll feel guilt, but you have to make your peace with it.
I set boundaries for myself, like trying not to travel more than once a month while classes are in session. But the best piece of advice I got was that your default answer should be "no."
I'll give you a concrete example: These days it's very easy for students to fire off long lists of questions about class by email, especially around exam time. But I am a two-fingered typist with 113 students in Business Associations and 106 in Mergers and Acquisitions. If I tried to answer email questions, it'd be a full time job. (Trust me, I have tried, and it is full time.) So I have a blanket policy in my syllabus stating that I don't answer substantive questions by email. Instead, I make my self available through office hours and a review session in each course.