Rashi: It is after Sukos.

Malbim: The prosecution [of Tzarei Yehudah and Binyamin] did not cease the Korbanos until the end of the second year. They began building in the second month of the second year. Then, the Tzarim wrote their prosecution. Surely the king's answer did not come before Shavu'os. It says below (7:8) that Ezra delayed four months on the road. They needed to wait for the Shali'ach to go [to Paras] and return.

Ibn Ezra: They are Kodesh via Beis Din (which is Mekadesh Rosh Chodesh).

Rashi: Anyone who offered a Nedavah, the Kohanim accepted it and offered it. They began offering on Tishrei 1, before the foundation of the Bayis was built.