One whose time is done in City, working with cross to bear (2-3)
I believe the answer is:
ex-con
'one whose time is done' is the definition.
(former convict who has served time)
I can't explain the rest of the clue.
(Other definitions for ex-con that I've seen before include "One who has served time" , "having defected from Tory party?" , "She used to serve porridge" , "One now free" , "Former jailbird" .)