zero hour
[noun]
Synonyms: juncture, contingency, crisis, crossroad(s), emergency, exigency, pass, pinch, strait, turning point

[TahlilGaran] English Synonym Dictionary ▲

ˈzero hour noun [singular]
the time when a military operation or an important event is planned to begin

[TahlilGaran] Dictionary of Contemporary English ▲

zero hour
1. the exact time when an attack or other military action will start
The air force planes waited until zero hour in order to start out on their bombing mission.

2. the time when an important decision or change is supposed to come
We waited for zero hour and the time when the new computer system was supposed to begin operating.

[TahlilGaran] English Idioms Dictionary ▲

zero hour
n.
1. The exact time when an attack or other military action is supposed to start.
Zero hour for the bombers to take off was midnight.
2. The time when an important decision or change is supposed to come; the time for a dangerous action.
It was zero hour and the doctor began the operation on the man.
On the day of the championship game, as the zero hour came near, the players grew nervous.

[TahlilGaran] English Idioms Dictionary ▲