When you say "song length" what do you mean by that? You can certainly change the scroll settings, tap the "Set as Default" button and that will be used for all new songs. If you are setting a fixed scroll duration, that would be have to be modified per song though. If you are saying you want MobileSheets to try to match a scrolling "pattern" dependent on the total number of pages, then no, you can't set that up at the moment as that's not supported. You can have scrolling start after 15 seconds, but if you are saying you want that amount of time to change depending on some aspects of the song (number of pages, page heights, etc), then that's not supported. If by "song" you are talking about an audio track, and you are wanting scrolling tied to the audio track playback, then that's not supported either.
Mike
Mike