Finally, Israel through Solomon’s leadership completed the building of the Temple of the Lord in Jerusalem. It was time to move the ark into the Holy of Holies,

Now Solomon assembled the elders of Israel and all the heads of the tribes, the chief fathers of the children of Israel, to King Solomon in Jerusalem, that they might bring up the ark of the covenant of the Lord from the City of David, which is Zion. Therefore all the men of Israel assembled with King Solomon at the feast in the month of Ethanim, which is the seventh month. So all the elders of Israel came, and the priests took up the ark. Then they brought up the ark of the Lord, the tabernacle of meeting, and all the holy furnishings that were in the tabernacle. The priests and the Levites brought them up (1 Kings 8.1–4). 

Unsurprisingly, this all happened in the seventh of the Jewish year. Seeing that seven means something to the Lord, and that the temple and the ark mean something to Him, of course we would find the children of Israel moving the ark into the completed temple during the seventh month.

This may not be as clear to some people for sure, and it is not something over which to argue, because either way, Solomon still built the temple and Israel still moved the ark into the temple.