8 o'clock is code between guys for one to signal to the other that he has a chance to hook up with a girl. The one who calls 8 O'clock then leave's the girl and the guy alone together and perfectly set up for a hook up. the guy who leaves has stopped himself from being a third wheel.
2 guys walking together with one girl
Girl flirting with guy 1
Guy 2: dude it's 8 O'clock, see ya later. (leaves and girl 1 and guy 1 start hooking up.)
Guy 2: Success and it's only 4.45pm