I want to write a song that's in 4, but has swinging notes - so I'm just writing tracks that fill up 24 of the slots instead of all 32. But in order to make it work in sequence I need the track to stop playing after the 24th slot and move on to the next segment in the song immediately. Is there a way to tell PICO-8 to do that? Of course I could just use all 32 slots and changing the measure's starting place depending on where I am, but I'd rather be more organized.

Is this something like what you're talking about? https://youtu.be/gwo9jY4ccB4?t=9m3s

Oh yeah! I totally forgot about that (I had watched that video but hadn't considered it since). Thanks! :)

Ok so I was actually concerned this wasn't going to work - turns out you need to have that empty channel on EACH segment of the track, or the length will change. However I realized that I can use the first channel for the empty track and just leave that first channel out of the music channel mask (mask = 2+4+8 = 14) and pico-8 still uses that channel to set segment length - and then use channel 0 for sound effects. Works great!