Matthew Poole and continuators on 2 Chronicles 29:17

17 Now they began on the first day of the first month to sanctifie, and on the eighth day of the month came they to the porch of the LORD; so they sanctified the house of the LORD in eight days, and in the sixteenth day of the first month they made an end .

In 16 Days purging the House, and Porch, and Courts, and all the Chambers belonging to the Temple. This is noted to imply partly the Universal Abuse and Defilement of all the Parts of it by Ahaz, which required so much time to remove; and partly the Diligence of the Priests in this Work.