Mistakes in time deserter included (6)
I believe the answer is:
errata
'mistakes' is the definition.
(an erratum is a mistake in a printed work)
'time deserter included' is the wordplay.
'time' becomes 'era' (era is a kind of time).
'deserter' becomes 'rat' (both can mean a traitor).
'included' means one lot of letters goes inside another.
'era' going around 'rat' is 'ERRATA'.
'in' acts as a link.
(Other definitions for errata that I've seen before include "mistakes in print" , "Noted mistakes" , "List of errors" , "Text mistakes" , "Mistakes in printing or writing" .)