Yoma 20: When the Cock Crows

And now for some aggadah: Why hasn't mashiach come? Presumably because of the promiscuity and sin that were getting in the way of his arrival. And the Satan will stand as an accuser against the people - in this case, that they shouldn't deserve mashiach. But on Yom Kippur, the Satan has no sway to argue against Bnei Yisrael. Plus, a new mishnah, bringing us back to the work of the altar, in this case, truly the dirty work of clearing out the ashes of the mizbeach. At the rooster crowing (if that's what this expression means - it's debated in the Gemara here). Though it was down earlier on festival days. Also, elaborating on exactly that question of whether the crier in the morning was a rooster or a person, to rouse the kohanim, and have them project for the people as well. Plus, sound carries more in the nighttime than during the day.