According to "Engishiki " (codes and procedures on national rites and prayers), Sakonefu (Left Division of Inner Palace Guards) took the duty from I-no-koku to Ne-no-koku (from nine o'clock in the evening to one in the morning), and Ukonefu (Right Division of Inner Palace Guards) did from Ushi-no-koku to Tora-no-koku (from one o'clock to five in the morning).
『延喜式』によれば、亥の刻・子の刻は左近衛府が、丑の刻・寅の刻は右近衛府が担当している。