Best time to work (3)
I believe the answer is:
top
'best' is the definition.
(top can mean the very best)
'time to work' is the wordplay.
'time' becomes 't' (abbreviation).
'to work' becomes 'op' (operation, work done in an operating theatre).
't'+'op'='TOP'
(Other definitions for top that I've seen before include "Better" , "Toy; uppermost point" , "Pinnacle" , "Highest, child's toy" , "Most successful" .)