Halakhah к Шкали́м 5:8

From the laws of the commandment [is] that which they, may their memory be blessed, said (Mishnah Shekalim 5:1), "There were fifteen appointees in the Temple: one was over the times," meaning to say to determine the time of the sacrifice. And he immediately envigorates them and says, "Priests, stand at your services; Levites, to the platform; and Israel, to serve!" And once they hear his voice, each one comes to his work. And specific priests and Levites would serve there. And it is like they, may their memory be blessed, said that Moshe and Shmuel the Seer and King David divided them into twenty four shifts, as it is found in Taanit 27a. And each shift would serve for a week and take turns in a cycle. And the head of the shift would divide all the men of the shift into clans. And each day of the week specific men would work, and the heads of the clans would divide specific men, each one to his service, and they would not be allowed to assist one another [in their tasks]. And so [too,] the Levites, the singer would not be allowed to help the gatekeeper; nor the gatekeeper, the singer. And of these fifteen appointees that we mentioned, we have already said that the first was appointed over the times; the second was appointed over the closing of the gates; third over the guards; fourth over the singers, etc., as it comes in the Mishnah. [This] and the rest of its details are in [various] places in the Order of Kedoshim and in Sifrei and in Mekhilta, as we have said above (see Mishneh Torah, Laws of Vessels of the Sanctuary and Those who Serve Therein 3).