We have a promo going that if you buy a gauge tester, when it ships you automatically get sent an email with a coupon code for 10% off any of the gauges and sending units we sell.  The discount code has an expiration, but as far as I can tell there is no way to set an expiration date on the rule that sends the email.

I could see use cases for both when a rule should start and when the rule should stop.