A measure of space and time (7)
I believe the answer is:
acreage
'a measure' is the definition.
(I have seen 'Measure of land' mean 'acreage' so perhaps 'measure' could also mean 'acreage')
'space and time' is the wordplay.
'space' becomes 'acre' (acre is a unit of area or space).
'and' says to put letters next to each other.
'time' becomes 'age' (an age is a period of time).
'acre'+'age'='ACREAGE'
'of' acts as a link.
(Other definitions for acreage that I've seen before include "Extent of ground" , "good quantity of land" , "Number of area measurements" , "Farm" , "Measure of land" .)