Errand and Zero hour

Errand noun - A short trip that is taken in the performance of a necessary task or mission.

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

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

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