It gets 'faster' and slower - the clock timer gets smaller as you take damage; the beat time slows down for the last 2 hits I think - it's more that at that point you've already lost due to not having the required moves to advance, so it's pretty much to reinforce the immersion/narrative.
I tried faster beat times during the development as well and you can't really tell the difference unless it gets unplayably faster - the base clock is 0.33s per beat or 180 bpm. Thanks for playing and thanks for the feedback!