Adverse criticism is harsh and, from time to time, guarded (9)
I believe the answer is:
stricture
'adverse criticism' is the definition.
(thesaurus)
'harsh and from time to time guarded' is the wordplay.
'harsh' becomes 'strict' (I've seen this before**).
'and' is a charade indicator (letters next to each other).
'from time to time' means one should take alternating letters (letters removed on a regular basis).
The alternate letters of 'guarded' are 'ure'.
'strict'+'ure'='STRICTURE'
'is' acts as a link.
(Other definitions for stricture that I've seen before include "Constraint" , "An adverse criticism" , "Abnormal medical narrowing" , "Restriction or stern criticism" , "Contraction of passage" .)