Time of strain (7)
I believe the answer is:
stretch
This clue is a double definition.
'time' is the first definition.
(I've seen this before)
'strain' is the second definition.
(I know that stretch is a more specific form of the action strain)
'of' acts as a link.
(Other definitions for stretch that I've seen before include "Period of time in prison" , "Elasticity, prison term" , "Strain" , "how much time one's been given" , "Make demands on; continuous expanse" .)