Albert Barnes Commentary Numbers 7:1

"And it came to pass on the day that Moses had made an end of setting up the tabernacle, and had anointed it and sanctified it, and all the furniture thereof, and the altar and all the vessels thereof, and had anointed them and sanctified them;" — Numbers 7:1 (ASV)

On the day that - that is, “at the time that,” . The presentation of the gifts in fact occupied twelve days, as the sequel shows.

The enactments set forth in the chapters from Leviticus 10 to Numbers 6 inclusive, were doubtless promulgated at various times between the consecration of the tabernacle and the departure from Sinai, but are for convenience set out connectedly. The contents of the present chapter are accordingly placed after them. The order pursued throughout is justly noted as one which would naturally suggest itself to a narrator who was contemporary with the events.