Up to work (4)
I believe the answer is:
till
I believe this clue is a double definition.
'up to' is the first definition.
(up to or till a certain time)
'work' is the second definition.
(to till is to work the land)
(Other definitions for till that I've seen before include "Farm - money drawer" , "cash container" , "Cultivate - cash drawer" , "Plough" , "not starting yet" .)