Choice about time of surgical procedure (9)
I believe the answer is:
operation
'surgical procedure' is the definition.
(I know that surgical procedure can be written as operation)
'choice about time' is the wordplay.
'choice' becomes 'option' (synonyms).
'about' is an insertion indicator.
'time' becomes 'era' (an era is a period of time).
'option' enclosing 'era' is 'OPERATION'.
'of' is the link.
(Other definitions for operation that I've seen before include "activity" , "management" , "Business" , "performance" , "battle" .)