Shut up near editor? It's about time! (8)
I believe the answer is:
closeted
'shut up' is the definition.
(I've seen this before)
'near editor? it's about time' is the wordplay.
'near' becomes 'close' (similar in meaning).
'editor?' becomes 'ed' (abbreviation).
'it's about' means one lot of letters go next to another.
'time' becomes 't' (abbreviation).
'ed' put after 't' is 'ted'.
'close'+'ted'='CLOSETED'
(Other definitions for closeted that I've seen before include "Concealed" , "Shut away for private talk" , "secret" , "Shut in small room" , "Do select, being in state of cautious privacy" .)