Perhaps "guidelines" is a better word. I have two of them, to ensure my sanity:

1. Taking a half day off on Thursdays shall commence in the afternoon rather than the morning (followed by work in the afternoon)
2. No taking Saturday off until homework is done. Then, if it's done, take Sunday off instead.

I should note that my current rules include swapping Thursday for Sunday, taking Thursday off entirely and working all day Sunday.