Deadline and Zero hour

Deadline noun - The point in time at which something must be completed.

Zero hour and deadline are semantically related in due date topic. In some cases you can use "Zero hour" instead a noun "Deadline".

Zero hour noun - A time or state of affairs requiring prompt or decisive action.

Deadline and zero hour are semantically related in moment of truth topic. You can use "Deadline" instead a noun phrase "Zero hour".