APAD: zero hour

Zero hour refers to the precise, scheduled time a military operation, critical event, or project begins, often synonymized with midnight or "H-hour". It also represents a critical decision moment, a 1945 historical milestone, a parliamentary session, a type of casual, on-call employment contract, and a tactical FPS video game. 

In historical, Refers to the end of WWII in Germany on May 8, 1945, representing a fresh start (Stunde Null).

Zero-Hours Contract: A type of employment contract in the UK with no guaranteed minimum hours, often used for on-call work; examples include on-call care assistants, substitute teachers, courier drivers, bank staff for the NHS, and gig economy workers like food deliverers. 

Video Game: A tactical first-person shooter (FPS) developed by M7 Productions and Attrito, set in Bangladesh, focusing on realistic, close-quarters combat.

In military operation: The exact time an operation commences (e.g., H-Hour).

example use

The negotiators worked through the night, knowing that midnight was the zero hour for a deal