Extent; duration (6)
I believe the answer is:
length
I believe this clue is a double definition.
'extent' is the first definition.
(I know that length is a type of extent)
'duration' is the second definition.
(synonyms)
(Other definitions for length that I've seen before include "End-to-end distance" , "Distance from one end of an object to the other" , "A brief swim" , "stretch" , "Measure (to which one should bowl?)" .)