Examines time and sets off (5)
I believe the answer is:
tests
'examines' is the definition.
(testing is a kind of examining)
'time and sets off' is the wordplay.
'time' becomes 't'.
'and' says to put letters next to each other.
'off' indicates anagramming the letters.
'sets' with letters rearranged gives 'ests'.
't'+'ests'='TESTS'
(Other definitions for tests that I've seen before include "Critically examines" , "Trials -- tribulations" , "Trials, exams" , "Trials to see if something works" , "International cricket matches" .)