I agree to an extent, but the problem is defining X before you send the email.

Let me put it this way: During the normal weekday, a 15 minute delay is probably sufficient. But coming home late on a Friday night, is 15 hours enough? Or, in some cases, 15 days?

So that's the question: how to define X ahead of time without knowing all conditions for which X applies? I suppose you could have date/time conditionals, but there would be instances where you probably violate your own rules.