When Russians tell what time it is, they often add "дня" ("of the day"), "вечера" ("of the evening"), "ночи" ("of the night"), or "утра" ("of the morning"):
Я проснулась в три часа ночи. (Literally: I woke up at three o'clock of the night.)
Я пришла в университет в полвосьмого утра. (Literally: I came to the university at half to eight of the morning.)
Перерыв заканчивается в три часа дня. (Literally: The break ends at three o'clock of the day.)
Вечеринка началась в пол-одиннадцатого вечера. (Literally: The party started at half to eleven of the evening.)
My question is this: Based on the linguistic convention in the Russian language, how long is the night?
For the purpose of this question, a time is considered to belong to the night if Russians add "ночи" rather than "утра, "дня," or "вечера" after it. For example, 2:39am belongs to the night because Russians say, "Я добралась домой в 2:39 ночи."
I am asking because I am unsure exactly where the boundaries of the night are in the Russian language.