Settler working one's time under officer (8)
I believe the answer is:
colonist
'settler' is the definition.
(I know that settler can be written as colonist)
'working one's time under officer' is the wordplay.
'working' becomes 'on' (on can mean working or activated).
'one's' becomes 'I's' (Roman numeral).
'time' becomes 't' (abbreviation).
'under' is a charade indicator (letters next to each other).
'officer' becomes 'col' (short for colonel).
'on'+'is'+'t'='onist'
'onist' put after 'col' is 'COLONIST'.
(Other definitions for colonist that I've seen before include "I'll settle" , "Coin slot (anag.)" , "Immigrant" , "Settler" .)