the.com/zero hour
The deadline so absolute it stopped bothering with a date.
means The precise moment an operation, attack, or plan is set to begin, after which everything else must follow on schedule.
from Military jargon from early 20th-century planning, where operations were timed backward and forward from a designated 'zero hour' — the H-hour of attack — so that troop movements, bombardments, and advances could be coordinated without revealing the actual clock time in written orders. It spread into general English for any make-or-break moment, especially during the World Wars when newspapers used it to describe offensives beginning at dawn.
- military origin
- Coined for scheduled start of an attack
- WWI usage
- Popularized during World War One planning
- no wiggle room
- Unlike deadlines, zero hour rarely moves
- modern drift
- Now means any make-or-break moment