I heard this today in a cd coursre I'm taking. The rule is 1/24 or 1/80. If your're writing a short story, sleep on it for 24 hours before deciding what to do with it. A longer piece -- give it 80 hours before editing it again and deterrming what to do.
Sounded reasonable to me.
Some of my edited and re-edited work is available at my website -- dianethomasplunk.com.