We might measure the passing of time by looking at what's changed. The passing of time is subjective, not objective. I can't be measuring the note itself. I must be measuring my memory of the note. When I measure time, I measure something in my own mind.
Time is subjective.
The sound of both is finished and has wafted away into the past. They no longer exist. I can only do this because they are both completed and are now things of the past. So it cannot be the syllables themselves that I measure, since they no longer exist. I must be measuring something which remains fixed in my memory.