Yoma, Chapter Three, Mishnah One
Our mishnah begins to describe the services performed in the Temple on Yom Kippur. The first thing done was to establish that it was light enough outside to slaughter the morning tamid (daily offering). This procedure was followed every day as well.
1) The officer said to them: Go out and see whether the time for slaughtering [the morning sacrifice] has arrived.
a) If it had arrived then he who saw it said: It is daylight!
2) Matitya ben Shmuel says: The whole east is light. Even unto Hebron? And he answered Yes.
Section one: After the second count, the first thing done was that the officer of the priests would tell another priest to go out and see if dawn had broken. The priest would stand on a high point in the Temple, look out and see if it had yet gotten light. The tamid offering can be offered as soon as it starts to get light, even before sunrise.
Section two: Matitya ben Shmuel was the officer in charge of the counts done in the Temple (see Shekalim 5:1). He would further interrogate the one who claimed to have seen daybreak. He wanted to know that a substantial portion of the sky had started to become light. The Talmud Yerushalmi explains that he mentions Hebron because that is where the patriarchs and matriarchs are buried. They would begin the day, therefore, by reminding God of the merit accrued to them by virtue of their being descendents of Abraham, Isaac and Jacob, as well as Sarah, Rivkah and Leah (Rachel was buried elsewhere).