I've literally had guys working 100 hr weeks only to turn around and have their Gov't counterpart stop mid-sentence in a meeting and say: "guys, have to cancel the rest of this, I'm at my 40. Let me know what you come up with over the weekend when we meet again on Monday."
I did work as a government civilian for about 3 years. It wasn't like that at all where I was. I frequently worked over 40 hours a week, and so did just about all of the others.
I'm not saying that to discredit your statement, as I have no doubt that there are those that do that. However, that hasn't been my experience.
I suppose it depends on the position. As an engineer, I/we were focused on getting things done on schedule because pilots were counting on us to be done. We weren't focused on the hours. I generally got in at 6am, left at 6pm ... although I did usually take close to 2 hours for lunch to go to the gym and workout.
When we were doing integrations, sometimes the schedule would dictate that I be there from midnight to 4am (because everybody can't integrate at the same time) but then be back in at 9am for pilot sessions and work until around 5 or 6, and then back in for another integration session from 2am-6am or something. Of course, that certainly wasn't the norm, just during heavy integration periods.