Albert Barnes Commentary 2 Chronicles 30:2

"For the king had taken counsel, and his princes, and all the assembly in Jerusalem, to keep the passover in the second month." — 2 Chronicles 30:2 (ASV)

In the second month - Hezekiah and his counselors reasoned that the permission found in the Law could, under the circumstances, be extended to all the people. It had proven impossible to complete the cleansing of the temple until after the fourteenth day of the first month had passed (2 Chronicles 29:17). Therefore, it was decided to postpone the festival to the fourteenth day of the second month, which allowed time for the priests to purify themselves and for a proclamation to be made throughout all Israel.