Harden after short time in occupation (6)
I believe the answer is:
tenure
'occupation' is the definition.
(I've seen this before)
'harden after short time' is the wordplay.
'harden' becomes 'enure' (I've seen this in another clue).
'after' means one lot of letters go next to another.
'short time' becomes 't' (abbreviation for time).
'enure' after 't' is 'TENURE'.
'in' acts as a link.
(Other definitions for tenure that I've seen before include "Dairy product" , "Incumbency" , "Neuter (anag)" , "Way of holding" , "Term of office" .)