An opportunity in the interval (5)
I believe the answer is:
break
I believe this is a double definition.
'an opportunity' is the first definition.
(I have seen 'Better opportunity' mean 'break' so perhaps 'opportunity' could also mean 'break')
'the interval' is the second definition.
(break is a kind of interval)
'in' is the link.
(Other definitions for break that I've seen before include "Time off working" , "Baker (anag.)" , "Interruption" , "that a billiards player wants as high as possible?" , "Fracture; holiday" .)