Deadline for when clock needs winding (4,5)
I believe the answer is:
time limit
'deadline' is the definition.
(I've seen this in another clue)
'clock needs winding' is the wordplay.
'clock' becomes 'time' (synonyms).
'needs winding' becomes 'limit' (I can't justify this - if you can you should believe this answer much more).
'time'+'limit'='TIME-LIMIT'
'for when' acts as a link.
Can you help me to learn more?
(Other definitions for time limit that I've seen before include "Prescribed term" , "Point before which something must be achieved" , "maximum duration" , "within which task must be done" , "Deadline" .)