Jamieson, Fausset and Brown on 2 Chronicles 30:21-24

21-24. the children of Israel ... kept the feast--The time appointed by the law for the continuance of the feast was seven days [Ex 12:15; 13:6; Le 23:6]; but in consequence of its having been allowed to fall so long into desuetude, they doubled the period of celebration and kept it fourteen days with unabated satisfaction and joy. Materials for the additional sacrificial meals were supplied by the munificence of the king and the princes.