Hezekiah Prays for Pardon After Intercalating Nisan in Nisan

It is written, "For Hezekiah had prayed for them, saying: May the LORD, the good one, grant pardon" and so forth (II Chronicles 30:18). Why did he ask for mercy upon himself? Because one may add a leap month only in Adar, yet he intercalated Nisan during Nisan itself, and Hezekiah did not hold by "This month shall be for you" (Exodus 12:2), which means this is Nisan, and so on. Hezekiah erred in the teaching of Samuel, for Samuel said: One does not declare the year a leap year on the thirtieth day of Adar, since that day is fit to be established as Nisan; but Hezekiah originally reasoned that we do not say "since it is fit to be established as Nisan." From where do we know that one does not count days to make up years? As it is said, "to the months of the year" (Exodus 12:2): months you count toward years, but you do not count days toward years. And from where do we know that one does not count hours to make up months? As it is said, "a month of days" (Numbers 11:20): days you reckon for months, but you do not reckon hours for months.