count·down
 /ˈkaʊntˌdaʊn/  noun  ,  pl   -downs [  count  ]
  1 : the act of counting down the number of seconds that remain before something (such as the launch of a rocket) happens
  — usually singular
   Begin the countdown.
   The engineers stopped the countdown because something was wrong with the engine.
  2 : the period of time before an important or special event — usually singular;
  — usually + to
   the countdown to summer vacation
   the steady countdown to war