Time to alter something (4)
I believe the answer is:
item
'something' is the definition.
(item means a thing)
'time to alter' is the wordplay.
'to alter' indicates an anagram.
'time' anagrammed gives 'ITEM'.
(Other definitions for item that I've seen before include "'One thing, poor mite (4)'" , "Object; piece" , "Indivual unit" , "Part of a list" , "point" .)