Attended a couple of “active shooter” seminars. In all these situations (gunman shooting people, hostage taking/killing, etc...) they say that from the time the LEs get the call to the time the LE types get on the scene and are ready to answer the question “What the F*CK is going on?” is 45 minutes. at the earliest. Then these LE teams decide what course of action must be taken and by whom, etc... 72 minutes seems about right.
So, when seconds count, the police are just 45-72 minutes away.