I'd propose that technically it starts at midnight, but that your definition falls consistent with A different respond to in this article that means It is based on how we come to feel about it. BVernon "Working day and night time" is much more ambiguous whether the "time" is intended https://andersonwm429.myparisblog.com/38494010/getting-my-night-gangnam-퍼펙트가라오케-karaoke-guide-to-work