The end of time, a brief moment recalled (5)
I believe the answer is:
omega
'the end' is the definition.
(last letter of the Greek alphabet)
'of time a brief moment recalled' is the wordplay.
'of' becomes 'o''.
'time' becomes 'age' (an age is a period of time).
'a brief' means to remove the last letter (a shorter or briefer version of the word).
'moment' becomes 'mo' (as in 'just a mo').
'recalled' says the letters should be written backwards (to recall can mean to bring something back).
'mo' with its last letter taken off is 'm'.
'age'+'m'='agem'
'agem' in reverse letter order is 'mega'.
'o'+'mega'='OMEGA'
(Other definitions for omega that I've seen before include "Athenian character" , "character from Athens" , ""The Alpha and the ___"" , "Last thing" , "Last letter of the Greek alphabet" .)