Green’s Dictionary of Slang

1. one who is up very late, after customers have been ‘turned out’ of everywhere else.

1826

Pierce Egan’s Life in London 18 June : ‘ The Finish.’ [...] This celebrated house of call for the turn outs, was kept, until a few years ago, by Mrs. Butler, who has retired from a publican’s life, although not from public life.

2. (US Und.) a discharge from prison [turn out v.² (2)].

1950		Goldin et al. DAUL 229/1: Turn-out, n. [...] 2. A discharge from prison; an acquittal by due process of law.
1952		C. Hamilton Men of the Und. 326: Turn-out, A discharge from prison or police custody.