Check out time for regime (4)
I believe the answer is:
diet
'regime' is the definition.
(eating regime)
'check out time' is the wordplay.
'check out' becomes 'die' ('check out' can informally mean to die).
'time' becomes 't' (abbreviation).
'die'+'t'='DIET'
'for' acts as a link.
(Other definitions for diet that I've seen before include "Food - parliament" , "Attempt to shift a few pounds" , "The kinds of food one eats" , "Range of food eaten" , "prescribed nourishment?" .)