Deserter in time making mistakes (6)
I believe the answer is:
errata
'mistakes' is the definition.
(an erratum is a mistake in a printed work)
'deserter in time' is the wordplay.
'deserter' becomes 'rat' (both can mean a traitor).
'in' indicates putting letters inside.
'time' becomes 'era' (era is a kind of time).
'rat' put within 'era' is 'ERRATA'.
'making' acts as a link.
(Other definitions for errata that I've seen before include "Listed errors" , "List of printed mistakes" , "Mistakes in printing or writing" , "Mistakes (Latin)" , "Feeling nausea" .)