Green’s Dictionary of Slang

being open late at night, or being active late at night.

1899		Ade Fables in Sl. (1902) 88: He wrote his Notice of the Night Owls’ performance from a Programme brought to him by the Head Usher at the Opera House.
1910		N.Z. Truth 16 Mar. 7/3: All they want is that the police will give the night-owl brigade [i.e. street prostitutes] the tip to shift into a street where their neighbours’ code of korals won’t clash with their own.
1916		J. Lait ‘Charlie the Wolf’ in Beef, Iron and Wine (1917) 27: They watched railroad stations, pawnshops, questionable apartment houses, night-owl restaurants, and even the hop joints.
1986		R. Campbell In La-La Land We Trust (1999) 162: My name is Crib Coxey, and I work the owl shift in the all-night drugs over to Common and Rampart.
1990		N. George ‘Superfly’ in Buppies, B-Boys, Baps and Bohos (1994) 118: Dap sells to and negotiates with nightowl shoppers on the fly tip.