Green’s Dictionary of Slang

(UK Und.) a criminal who has served time in jail; often in combs, e.g. first-timer under first adj., short-timer n. (2)

1884		Leicester Chron. 14 June 12/1: The prisoner in the cell next to him was a bad character — a ‘third timer’.
1924		S. Scott Human Side of Crook and Convict Life 19: There were three vanloads of us — young men and old men, novices and ‘timers’, all huddled in together.
1937		‘Boxcar Bertha’ Sister of the Road (1975) 145: I just got to beat this rap [...] I’m a four-timer, and if I’m convicted I’ll be sent to the penitentiary for life.
1949		Monteleone Criminal Sl. (rev. edn).
1990		A. Dangor Z Town Trilogy 150: Gwan, you snotkop, don’t lol with timers .