convict hour

convict + hour, as criminal activities might be expected to take place in the quiet hours of the night.

the convict hour

1. Around four to five o'clock in the morning.
   • 1951 Autumn, Saul Bellow, “The Coblins”, in The Sewanee Review, volume 59, number 4, The Johns Hopkins University Press, →JSTOR, page 651:

     At the convict hour between four and five when even those with the least to fear are darkened and sober, and back away from waking.

     Note: "The Coblins" was chapter 2 of The Adventures of Augie March, (Viking Press, 1953)

   • 2008, Laura Pedersen, The Big Shuffle, Random House:

     The beauty of four in the morning is not its furnishings and décor, but its aim-lessness and stolen quality. I suppose that's why Cappy always calls it “The Convict Hour.”