Dastardly so-and-so cutting long time lapses (6)
I believe the answer is:
errata
'lapses' is the definition.
(plural of 'eratum' - an eratum is a mistake)
'dastardly so-and-so cutting long time' is the wordplay.
'dastardly so-and-so' becomes 'rat' (rat can mean a scoundrel).
'cutting' means one lot of letters goes inside another (some letters cut their way into a word).
'long time' becomes 'era' (a long period of time).
'rat' inserted into 'era' is 'ERRATA'.
(Other definitions for errata that I've seen before include "List of printed mistakes" , "Misprints in a book" , "Mistakes in printed work" , "Text mistakes" , "Listed errors" .)