When entering in notes to make a song you need to enter in a start time for that note. This start time obviously increases as you progress though the song, however I was wondering by what increments does the number that represents the start time increase by. Beats, half-beats, quarter-beats, etc.?
Honestly, there are better ways to make a song file than by manually typing everything into a text file. I would recommend trying to get Composer, which makes it a lot easier to do.
As to the actual question itself, I have utterly no clue. Maybe someone else can help you out there if you really want to do it manually.
The #GAP measures the time from the beginning of the song to beat number 0 in milliseconds. The note positions are measured in beats after the gap. Technically, you can create notes that start in the negative, but those will glitch up the song. The length of a beat is mesured by 60/BPM, in seconds.