MusicTempo

MusicTempo -> beatsPerMinute

specifies playback tempo in beats per minute for symbolic music.

The default is 120 BPM. A quarter note therefore lasts 60 / beatsPerMinute seconds.

Apply tempo to a MusicScore:

MusicScore[
  {
    MusicVoice[{
      MusicNote["C4", 1/4],
      MusicNote["E4", 1/4],
      MusicNote["G4", 1/2]
    }]
  },
  MusicTempo -> 90
]

It can also be supplied to Sound when playing music events directly:

Sound[
  {MusicNote["C4", 1/4], MusicNote["G4", 1/4]},
  MusicTempo -> 72
]

The active tempo is shown in the player metadata when it is available to the frontend. Tempo on a score, voice or measure is inherited by its events unless overridden by a more specific container.