Scoundrel, in the course of time, makes mistakes (6)
I believe the answer is:
errata
'mistakes' is the definition.
(erratum is a kind of mistake)
'scoundrel in the course of time' is the wordplay.
'scoundrel' becomes 'rat' (I've seen this in other clues).
'in the course of' means one lot of letters goes inside another.
'time' becomes 'era' (I've seen this before).
'rat' put into 'era' is 'ERRATA'.
'makes' is the link.
(Other definitions for errata that I've seen before include "Feeling nausea" , "Mistakes in printed proofs" , "List of errors" , "Misprints in a book" , "Mistakes in printed matter" .)