Time to compose a poem with perfect ending (5)
I believe the answer is:
tempo
'time' is the definition.
(tempo is a kind of time)
'compose a poem with perfect ending' is the wordplay.
'compose' indicates an anagram.
'with' means one lot of letters go next to another.
'ending' suggests the final letters (the ending of the word).
The final letter of 'perfect' is 't'.
'poem' is an anagram of 'empo'.
'empo' put after 't' is 'TEMPO'.
'to' acts as a link.
(Other definitions for tempo that I've seen before include "Time (music)" , "Speed of 3A" , "(Musically) the speed to be played" , "Pace of a musical piece" , "Rate and rhythm in music" .)