hour of the Rat; midnight period
Archaic term for the time around midnight, roughly 11pm–1am or midnight–2am in the traditional Chinese-derived time system. Used in historical or literary contexts.
In the old time system, the hour of the Rat corresponds to around midnight.
From the traditional Chinese zodiac-based time system, where 子 (the Rat) represents the first of the twelve double-hours, covering the middle of the night.