Judge doubtful for a moment (5)
I believe the answer is:
jiffy
'a moment' is the definition.
(I've seen this before)
'judge doubtful' is the wordplay.
'judge' becomes 'j' (abbreviation for judge).
'doubtful' becomes 'iffy' (I've seen this before).
'j'+'iffy'='JIFFY'
'for' acts as a link.
(Other definitions for jiffy that I've seen before include "Brief moment" , "Two shakes of a lamb's tail?" , "Very short moment - type of bag" , "Split second" , "An instant" .)