What is "b'Yom He'asoso"?
Radak: On the day that it will be finished.
What is the significance of offering Korbanos when it is finished?
Radak: This is like they did in the Mishkan on the eighth day of the Milu'im.
Malbim: We inaugurate a new Mizbe'ach only with the morning Tamid (Menachos 4:4). Here will be a general Chinuch of the entire Mikdash! There was a Chinuch in the days of Ezra; it was a Hora'as Sha'ah (Hashem told Nevi'im at the time), and different. They knew that it is not the Bayis that Yechezkel prophesized about, for Hashem promised to revive Yechezkel (a Kohen), and he will inaugurate it 1 ! Also Chinuch ha'Mishkan had Korbanos that applied only at that time 2 .
They already knew [that Yechezkel did not prophesize about Bayis Sheni] while building it, for they did not build it exactly like it says here! Malbim's words require investigation. (PF)
Rashi (Shemos 29:14, 22-23): We find an outer Chatas that is totally burned, offering the thigh with the Emurim, and Haktarah of Lechem that accompanies a Korban only in the Milu'im. (Also, we find voluntary Chata'os, Ketores and Korbanos on Shabbos only in Chanukas ha'Nesi'im. - PF)
What blood will they throw on it?
Radak citing Targum Yonasan: The blood of the Korbanos.
Malbim: Via the inauguration it will be proper to offer on it [limbs of Olos and] blood of Korbanos.
