The more time you have before an event, the greater the number of lives that can be saved assuming of course the authorities are competent and the evacuation carried out in an ordered fashion. Clear, concise and truthful information has to passed to the intended evacuees, no matter how dire that information is as even minutes or seconds warning can contribute to saving some lives that would otherwise be lost.

Of course knowing how to naturally form an orderly queue is more of a cultural issue.

http://en.wikipedia.org/wiki/Mount_Pinatubo#Evacuation

http://en.wikipedia.org/wiki/1975_Haicheng_earthquake