Line put in joke with time set back part of Ireland (7)
I believe the answer is:
'part of ireland' is the definition.
(I've seen this before)
'line put in joke with time set back' is the wordplay.
'line' becomes 'l' (used when specifying particular lines from a poem).
'put in' is an insertion indicator.
'joke with' becomes 'kid' (I've seen this in another clue).
'time' becomes 'era' (era is a kind of time).
'set back' says the letters should be written in reverse.
'era' backwards is 'are'.
'l' placed within 'kid' is 'kild'.
(Other definitions for kildare that I've seen before include "division in Ireland" , "Irish county near Dublin" , "doctor from long ago" , "somewhere in Ireland" , "part of Ireland" .)