Alter arrangement afterwards (5)
I believe the answer is:
later
'afterwards' is the definition.
(I know that afterwards can be written as later)
'alter arrangement' is the wordplay.
'arrangement' is an anagram indicator.
'alter' is an anagram of 'LATER'.
(Other definitions for later that I've seen before include "at a subsequent point" , "When to see you?" , "Following" , "In due course" , "After a given point in time" .)