Green’s Dictionary of Slang

1. (US prison) to reach the end of one’s sentence; thus short-timing n. and adj. [time n. (1)].

1975		E. Torres Carlito’s Way 45: When you’re short-timin’, waitin’ on your parole, the cons will provoke you to fight.
1994		T. Willocks Green River Rising 24: That short-timing bastard’d tell us anything.

2. in fig. use of sense 1, to take the short view as regards one’s lifestyle.

1975

E. Torres Carlito’s Way 71: I’m short-timing in this world and any way I get by is okay with me.

3. to have sex with a prostitute for a short time (rather than a whole night) [short time n. (1)].

1977

L. Heinemann Close Quarters (1987) 258: To short-time Claymore Face [...] is to guarantee a sovereign cure for everything from sweat pimples to tumorous blood clots.