Bounds of empire shifting over time? I’m not sure (9)
I believe the answer is:
perimeter
'bounds' is the definition.
(bounds can mean the perimeter around a place)
'empire shifting over time? i'm not sure' is the wordplay.
'shifting' indicates anagramming the letters.
'over' is a charade indicator (letters next to each other).
'time?' becomes 't' (abbreviation).
'i'm not sure' becomes 'er' (expression of hesitation).
'empire' with letters rearranged gives 'perime'.
'perime'+'t'+'er'='PERIMETER'
'of' acts as a link.
(Other definitions for perimeter that I've seen before include "Outer boundary" , "edge" , "Prime tree (anag.)" , "Exterior of a plane figure" , "Enclosing boundary" .)