It's up to time in cultivation (7)
I believe the answer is:
tillage
'cultivation' is the definition.
(I know that cultivation can be written as tillage)
'it's up to time' is the wordplay.
'it's up to' becomes 'till' (up to or till a certain time).
'time' becomes 'age' (an age is a period of time).
'till'+'age'='TILLAGE'
'in' acts as a link.
(Other definitions for tillage that I've seen before include "Work on land" , "Cultivation of crops" , "Preparing for cultivation" , "Cultivation of the land" , "Farmers undertake it" .)