Leviticus 8:33
And ye shall not go out of the door of the tabernacle of the congregation in seven days, until the days of your consecration be at an end: for seven days shall he consecrate you. And ye shall not go out of the door of the tabernacle of the congregation in seven days, until the days of your consecration be at an end: for seven days shall he consecrate you.
The consecration of the priests was appointed to last seven days. Each of those seven days was marked by its own special consecration ceremonies. Only when that seven-day period was complete did the priests enter upon their ministry, beginning their service on the eighth day.