Zero hour

[مستر رمضان عيسى]

Zero hour
The time when something important is to begin is zero hour.
Zero tolerance
If the police have a zero tolerance policy, they will not overlook any crime, no matter how small or trivial.
Zigged before you zagged
If you did things in the wrong order, you zigged before you zagged.
Zip it
This is used to tell someone to be quiet.
Zip your lip
If someone tells you to zip your lip, they want to to shut up or keep quiet about something. ('Zip it' is also used.)