Tryst and Zero hour

Tryst noun - An agreement to be present at a specified time and place.

Zero hour and tryst are semantically related. In some cases you can use "Zero hour" instead a noun "Tryst".

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

Tryst and zero hour are semantically related. Sometimes you can use "Tryst" instead a noun phrase "Zero hour".