It changes around 11:40. Not the music, the room.
The first set is a performance. People came on purpose. They sit forward; they applaud after solos because that is what you do at a jazz show. The second set is a conversation. The third is something else. By the third set, the audience has self-selected: the people still here are either locked in or asleep, and you can usually tell which from the bar.
The room shrinks. The light gets kinder to mistakes. The drummer stops counting in and starts looking up.
There is a thing that happens, and I do not know how to describe it without sounding like the kind of musician I make fun of, where the band stops trying to play for anyone. Not because the audience does not matter. Because the audience has become part of the band. The four people at table six are listening so hard they are doing some of the work. You can hear them in the room. You play differently when you can hear someone listening.
Most of the recordings I love are late sets. Not because the playing is better. Because the room is better. There is an honesty that only shows up after the people who came to be impressed have gone home.
If you ever get the chance to play the last set of a long night, take it. You will find out what you actually sound like.
I do not think this scales. I do not think you can manufacture the late set in a studio, although I have tried, and the closest I have come is recording at four in the morning with the lights off. The body does not know it is being recorded. The body just knows it is tired and it is late, and there is a song in the way.