You can upload audio files on Mastodon. The upload works just like attaching images or videos, but you select a sound file instead. You can also attach artwork by clicking Edit and then Choose Image.
There is no time limit on audio, but it has to be within the file size limit on your server (usually 40MB).
Supported formats are MP3, OGG, WAV, FLAC, OPUS (rename it to end in .ogg), AAC, M4A or 3GP.
(Music is "Modern Technology" by Mokka Music, used under CC-By licence)