How does opcode 363 (cancel song) work?

How does the new "cancel bard song on movement" opcode work?

With the Shaman, it is attached as an effect in the Shaman dance. There, it is set to timing mode 1 (instant/limited) with a duration of 3. What does that "duration" mean in this context?

EDIT - and what does the "movement rate" value signify in the parameter1 field?

I'd like to use this opcode with a bard song I'm working on, but I'm having a bit of trouble. For whatever annoying reason, bard song does not kick in right away. It can kick in anywhere from "pretty quickly" to a few seconds after I press the button.

When I put the song cancellation effect from Shamans into my song's .SPL file, it has a problem: if I move around, the cancellation can trigger before the song itself triggers. So in those cases it doesn't do much cancel bard song, as much as prevent it. For reasons I won't get into now, I want to make sure that when I press the bard song button it definitely takes effect. Even if only briefly.

Can the cancellation-on-movement opcode be adapted to this purpose? Can I make it kick in later - like, 6 seconds later? Does it work with timing mode 4 (delayed/permanent)?