I'd personally suggest that technically it starts off at midnight, but that the definition falls consistent with One more reply in this article that suggests it's based upon how we come to feel about it. BVernon "Working day and night time" is much more ambiguous if the "time" is intended https://danteowepl.dgbloggers.com/38384227/night-gangnam-퍼펙트가라오케-karaoke-guide-no-further-a-mystery