I'll dance once for every thread you make.
I would say, rather then have a activation time limit, make the "/dance *" command join in synchronized dance with anyone already dancing in the vincinity. Same could be done for all the music./dance = makes you start dancing, as the command works right now
/dance * = all players who enter this command within the same 2-3 seconds start dancing in synchronously
This is how Guild Wars 2 works. Maybe we could even add synchronized lute and flute playing.