Magma requires 30 seconds that’s how long the preview lasts. However, there are some tricks you can try, all of which require tweaking the CON after Magma compiles it.
You can edit the DTA and change the preview start and stop times, so that the preview is something other than 30 seconds. That way you at least don’t hear all that silence when selecting the song from the song menu.
You can then inject a MIDI with the EVENT track’s [end] marker moved to the appropriate time so that the game will actually stop the song before playing 27 seconds of silence. The game may still behave oddly; I honestly don’t know, but it’s worth a shot.
You are about to leave Rhythm Gaming World and access the external songs DB. While no song or file sold for commercially available videogames is hosted there and only fan generated content is allowed, Rhythm Gaming World has no direct control over the database and no files are hosted here. Alright, we had to made you aware of this, now you can visit the database!