What does 2 Chronicles 29:17 mean?

They started purifying everything on the first day of the first month. By the eighth day, they reached the porch of the Lord’s temple. They spent another eight days purifying the Lord’s temple itself, and finished on the sixteenth day of the first month. 2 Chronicles 29:17 - Modern Text Bible

(The whole process took sixteen days. They worked methodically, starting from the outside and moving in, making sure every part of the temple was made clean.)