Subsequently alter arrangement (5)
I believe the answer is:
later
'subsequently' is the definition.
(subsequently means later on)
'alter arrangement' is the wordplay.
'arrangement' indicates anagramming the letters.
'alter' anagrammed gives 'LATER'.
(Other definitions for later that I've seen before include "Subsequently" , "goodbye" , "After a given point in time" , "after the rest?" , "Following" .)