2 Chronicles 29:17

Now they began on the first day of the first month to
sanctify
Either of the reign of King Hezekiah, or rather of the year; the month Ab or Nisan, as the Targum expresses it: and on the eighth of the month came they to the porch of the Lord;
they seem to have begun cleansing the inner part of the temple first, and so came forward until they came to the porch which led into it: so they sanctified the house of the Lord in eight days;
the holy place, and it may be the most holy place, and the court of the priests: and on the sixteenth day of the first month they made an end;
it took them eight days more to cleanse the outward porch, and the buildings and chambers belonging to the temple; according to Jarchi, it required so much time, because Ahaz had framed pictures of idols upon the walls of the temple, which could not be defaced sooner.