John Gill Commentary Exodus 29:35

"And thus shalt thou do unto Aaron, and to his sons, according to all that I have commanded thee: seven days shalt thou consecrate them." — Exodus 29:35 (ASV)

And thus shall you do unto Aaron, and to his sons
For their consecration, washing, clothing, anointing them, sprinkling blood upon them and their garments, and offering sacrifice for them:

according to all things which I have commanded you ;
no one thing was to be omitted, and we find they were carefully and punctually observed, (Leviticus 8:1–36)

seven days shall you consecrate them :
so long the rites and ceremonies of the consecration were to be performing, that they might be thoroughly used to the putting on of their garments, and the offering of sacrifices as they saw performed by Moses; and in all respects be fitted for the discharge of their office: the Jewish writers generally say that seven days were appointed, that a sabbath might pass over them.