Judge with a Parisienne for thirty days (4)
I believe the answer is:
june
'thirty days' is the definition.
'judge with a parisienne' is the wordplay.
'judge' becomes 'j'.
'with' means one lot of letters go next to another.
'a parisienne' becomes 'une'.
'j'+'une'='JUNE'
'for' acts as a link.
(Other definitions for june that I've seen before include "Month named after Jupiter's wife" , "Spring/summer month" , "Month of our summer solstice" , "The "flaming" month?" , "some time" .)