Holy shit grinding this was the most painful thing ever, you basically cannot restart on the boss as that loses 6.5s because the timer starts early XD So what you have to do is go through the whole story again with the cutscenes and all and get your Perfect Chaos time first try so that's pretty funny, sub 1 is doable but i'll leave that for an other time if i come back to it

TL;DR : i grinded this so you don't have to :)