O-silly hundred
(n.) Very early in the morning. Stupid o’clock, O-dark hundred, O-four fuck’s sake, Dark o’clock, Crack of a sparrow’s, Early doors
The Aircrew Dictionary (of unacceptable cliche and overused phrases)
(n.) Very early in the morning. Stupid o’clock, O-dark hundred, O-four fuck’s sake, Dark o’clock, Crack of a sparrow’s, Early doors