Read the in-game clock without confusing it with local real-world time.
This clock runs six game days per real day: a complete cycle lasts four real hours. Night is game time 00:00 to before 06:00, lasting one real hour; daylight lasts three. One game hour equals ten real minutes. Day/night changes notify the spawn manager and relevant effects.
The clock reference is based on midnight in the server timezone. Your local clock or a screenshot from another server cannot establish the current game hour. A day/night transition does not prove that every NPC or boss uses a day/night spawn rule.