Republic of Ireland, about 2003, just before sunrise
In July of 2008, the government banned "off-licence" sales after 10 P.M. no alcohol take-away, after that hour.
This legislation (for the safety of the kids, who were already disallowed from buying alcohol) put an end to impromptu drinking after hours, at least officially.
There seems to be an almost mystical understanding amongst my friends in Kilkenny that 4:30 in the morning is the normal time to go home.
It's not that nobody goes home earlier for God's sake, nobody can go mad all the time and it's not that nobody goes home later, because you hear about folks who see the sun come up.
But, with uncanny regularity, the good times last until 4:30 in the morning. At about that time, somebody will start to wonder what time it is or just as spontaneously, simply decide that it's time to go. Usually and for as little reason this will start an exodus. It's just time to go. Nobody knows why.
The "dawn chorus" is a broadly-distributed early-morning chatter of songbirds beginning well before sunrise and lasting until the bright of day.