Surgery seen as possible choice over time (9)
I believe the answer is:
operation
'surgery' is the definition.
('operation' can be a synonym of 'surgery')
'possible choice over time' is the wordplay.
'possible choice' becomes 'option' (I've seen this before).
'over' indicates putting letters inside.
'time' becomes 'era' (I've seen this before).
'option' enclosing 'era' is 'OPERATION'.
'seen as' acts as a link.
(Other definitions for operation that I've seen before include "military undertaking" , "Act of surgery" , "Surgical or military procedure" , "To one pair (anag.)" , "activity" .)