golden hour

noun
  1. the first hour after a serious accident, when it is crucial that the victim receives medical treatment in order to have a chance of surviving
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012