Green’s Dictionary of Slang

1. to work or socialize at night.

1878		H.B. Stowe Poganuc People 7: Little girls like you must go to bed early. They can’t be up ‘night-hawkin’, and goin’ round in the cold.
1913		Day Book (Chicago) 29 Dec. 24/1: Now Waddell, victim of tuberculosis, is paying the price of his years of night-hawking and revelry.
1930		W. James Lone Cowboy 172: I was hired, hired to nighthawk.

2. to drive a cab at night.

1949

W.R. Burnett Asphalt Jungle in Four Novels (1984) 255: Nighthawking’s bad enough any place. But around the square a man’s not safe.