Crossword Genius

Time flies? It might! (4)

Ross

I believe the answer is:

bird

'time' is the definition.
(both are slang for a prison sentence)

I cannot understand how the remainder of the clue works.

(Other definitions for bird that I've seen before include "Creature - time in prison" , "chat, perhaps?" , "Dawn chorus etc - book by Sebastian Faulks" , "Flier - spell in prison" , "Flying creature" .)

I've seen this clue in The Guardian.
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