I'm assuming you've seen this, but if you haven't: http://ea-spouse.livejournal.com/274.html
If people are genuinely excited about working for you and choose to put in long hours, you thank them, reward them for their efforts and remind them to go home, eat, sleep, spend time with their family, etc. Some people have higher thresholds, some people lower, so I don't think you can enforce any particular rule straight across the board. But you can provide a healthy environment. If my husband ever became a tyrant, he wouldn't be my husband anymore. He knows that :)