Occasionally, then, site's revealing stretches (5)
I believe the answer is:
tests
'stretches' is the definition.
(stretch can mean to test or put pressure on)
'occasionally then site's' is the wordplay.
'occasionally' means one should take alternating letters.
'then'+'sites'='thensites'
The alternate letters of 'thensites' are 'TESTS'.
'revealing' is the link.
(Other definitions for tests that I've seen before include "Trials, exams" , "Critically examines" , "Trials -- tribulations" , "Major cricket matches" , "Trials to see if something works" .)