How many work hours per week is too much before burnout?

I've a 35 min commute to work each day, and I usually work 9-7pm every day, sometimes more (like 55-60 hours per week), occasionally a little less (like 42 hours is a great week but rare). It's been like this for several years and I'm getting tired of it... and it seems like everybody I know works less. I'm worried about whether I'd be able to have kids and be a mom with this job - it would be impossible to leave at 5 or 5:30. Nobody in my office has kids, so everybody works these hours or longer. How do people do it? And sorry to sound whiny, but it's been a rough day! :)