English minister's retiring at any time (4)
I believe the answer is:
ever
'at any time' is the definition.
('ever' can be a synonym of 'at any time')
'english minister's retiring' is the wordplay.
'english' becomes 'e' (abbreviation).
'minister' becomes 'rev' (I've seen this before).
'retiring' says the letters should be written in reverse.
'rev' backwards is 'ver'.
'e'+'ver'='EVER'
(Other definitions for ever that I've seen before include "Always and permanent" , "Veer away endlessly" , "At all times, always" , "On any occasion" , "Possibly" .)