Time to admit informer’s mistakes (6)
I believe the answer is:
errata
'mistakes' is the definition.
(an erratum is a mistake in a printed work)
'time to admit informer's' is the wordplay.
'time' becomes 'era' (era is a kind of time).
'to admit' indicates putting letters inside.
'informer' becomes 'rat' (synonyms).
'era' enclosing 'rat' is 'ERRATA'.
(Other definitions for errata that I've seen before include "List of printing mistakes" , "Publishing mistakes" , "Feeling nausea" , "Mistakes in printed matter" , "Corrigenda" .)