@Prince of Seraphs Apollo is God of Song. Michael had the power to use magic songs. By playing his enchanted instruments and playing the right songs he can use magic. The more powerful the song the more time he needs however with his brother Peter they can do more power song magic they wouldn't be able to normally do alone.
That I got, but magic music to reverse time? Isn't that a little godmoddish. I get that Apollo is the god of music (among other things) so his sons and daughters would have musical proficiency with some level of godly power tied to that. However if there's a magic song that replicates the power of the King of the Titans doesn't that sort of imply there's a magic song that can duplicate the abilities of any demigod or demititan?