How do I create an escalation rule that fires immediately?

I want to use escalation emails as beeper activations to meet an SLA for customer support.  To do this, I need to create an escalation rule and territory that immediately escalates a case when it is submitted.  I tried the obvious, which was to create a rule that fired when time since case creation was zero.  This doesn't work (or more strangely it works about 1 out of 10 times or less.)   The one time it worked, the escalation happened 20 minutes after the case was created - 20 minutes of my customer's time that is wasted.   I'd like to