zero hour

”zero hour”
the scheduled time for the start of an operation or action, especially a combat operation of great size; the time at which something, especially some type of military activity, is planned to begin
زمان شروع اتفاق یا برنامه مهمی
Example : Look at the clock! Our team needs to leave now if we’re going to arrive at the client’s office on time. We’ve got to win this deal. Guys, it’s zero hour