High temperature not starting 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')
'high temperature not starting' is the wordplay.
'high temperature' becomes 'fever' (I've seen this before).
'not starting' means to remove the first letter.
'fever' with its first letter removed is 'EVER'.
(Other definitions for ever that I've seen before include "In perpetuity" , "Eternity" , "On any occasion" , "Always and permanent" , "Possibly" .)