Sam Smith o'clock
On a night out, Sam Smith o'Clock is the point at which the first person leaves. It can be at any time during the night and any individual, but will always be known as Sam Smith o'clock.
Person 1: Did you know Jamie's gone home?
Person 2: Noway! - I guess it's Sam Smith o'clock!
Person 2: Noway! - I guess it's Sam Smith o'clock!