Voila! A tempo! (6)
I believe the answer is:
presto
'tempo' is the definition.
(musical tempo)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for presto that I've seen before include "Very fast (mus.)" , "In quick tempo (mus.)" , "Moving quickly" , "Immediately" , "hey......,cries the magician" .)