A pop duet released after 1st of May charted (6,3)
I believe the answer is:
mapped out
'charted' is the definition.
('map out' can be a synonym of 'chart')
'a pop duet released after 1st of may' is the wordplay.
'released' is an anagram indicator (letters released from their original order).
'after' means one lot of letters go next to another.
'mst of may' becomes 'm' (1st letter of 'may').
'pop'+'duet'='popduet'
'popduet' anagrammed gives 'ppedout'.
'a'+'ppedout'='appedout'
'appedout' after 'm' is 'MAPPED OUT'.
(Another definition for mapped out that I've seen is " planned".)