Rodent in time makes mistakes... (6)
I believe the answer is:
errata
'mistakes' is the definition.
(an erratum is a mistake in a printed work)
'rodent in time' is the wordplay.
'rodent' becomes 'rat' (rat is a kind of rodent).
'in' is an insertion indicator.
'time' becomes 'era' (an era is a period of time).
'rat' put inside 'era' is 'ERRATA'.
'makes' acts as a link.
(Other definitions for errata that I've seen before include "Mistakes in printing or writing" , "List of printing mistakes" , "Listed errors" , "List of text corrections to be made in a publication" , "corrected mistakes" .)