Reminder - the writer of this puzzle takes a little time (4)
I believe the answer is:
memo
'reminder' is the definition.
(I've seen this before)
'the writer of this puzzle takes a little time' is the wordplay.
'the writer of this puzzle' becomes 'me' (the person setting the crossword).
'takes' says to put letters next to each other.
'a little time' becomes 'mo' (I've seen this in other clues).
'me'+'mo'='MEMO'
(Other definitions for memo that I've seen before include "In brief, a note of events" , "Inter-office note" , "Short note or message" , "diplomatic communication?" , "It will remind" .)