late night to early morning; the small hours
Historical term for the period from midnight until early morning, roughly corresponding to the modern 'small hours'. Not used in everyday modern timekeeping.
around 4am
More specifically, the time around 4am, corresponding to the hour of the Tiger (寅の刻) in the traditional Japanese clock. This is a narrower interpretation of 後夜.
See also: 寅の刻
後夜 refers to the period from about the hour of the Ox to the hour of the Tiger in the old time system.
In classical texts, 後夜 is equated with the hour of the Tiger, i.e., around 4 a.m.
Composed of 後 (after, later) and 夜 (night), literally 'later night'. The term originates from the traditional Japanese timekeeping system where the night was divided into periods; 後夜 designated the latter part of the night.