Alter, for a change, at some future time (5)
I believe the answer is:
later
'at some future time' is the definition.
(I've seen this in another clue)
'alter for a change' is the wordplay.
'for a change' indicates an anagram.
'alter' with letters rearranged gives 'LATER'.
(Other definitions for later that I've seen before include "Alter (anag.)" , "At a subsequent time" , "Afterward, subsequent" , "Eventually" , "after the rest?" .)