Radak: It is the beginning of the third year. Also "mi'Ktzei Sheva Shanim Teshalchu Ish Es Avdo" (Yirmeyah 34:14) and "mi'Ketz Sheva Shanim Ta'aseh Shemitah" (Devarim 15:1) are the beginning of the seventh year. Melech Ashur came in the fourth year of Chizkiyah, which was Hoshe'a's seventh year, and conquered it in the sixth year of Chizkiyah, which was Hoshe'a's ninth year. [The siege was] two years, and it is called "mi'Ktzei Shalosh Shanim."

Targum Yonasan: It is the end of the third year. Radak - he must hold that "the fourth year" [of Chizkiyah] and "the seventh year" [of Hoshe'a] refer to the beginning of the fourth year and seventh year (and the sixth year of Chizkiyah and the ninth year of Hoshe'a refer to the ends of those years - PF).