Or HaChaim on Exodus 24:1/אור החיים על שמות כ״ד:א׳

1 ואל משה אמר, And He had said to Moses (previously), etc. It appears that this paragraph was revealed immediately after the revelation at Mount Sinai but was inserted in the Torah only here. There is no point in citing numerous arguments proving this theory. Ibn Ezra, Nachmanides, and Rashbam are all agreed that the paragraph must have been revealed at the time of the revelation.

2I have seen an undisputed theory in the Mechilta according to which Moses built an altar on the fifth day of Sivan (a day before the revelation) and that this was the altar mentioned in verse 4, and that he concluded a covenant with the people confirming their adherence to the seven Noachide laws as well as to the statutes he had taught the people at Marah (15,25). Some rabbis hold that the covenant Moses made the people swear to at that time covered all the laws revealed in the Torah till the end of the Book of Leviticus. According to these sages all those laws had to be revealed before the revelation at Mount Sinai. Seeing the people had not been asked to enter into a covenant concernig any of G'd's laws prior to this, we must assume that Moses tested them to see if they were willing to enter into such a covenant of their own free will concerning all of the commandments which had already been revealed even though it had not been G'd Himself who had given them these commandments. Perhaps we find a hint of all this in G'd telling Moses in 19,3:"and tell the children of Israel!" Shabbat 86 understands this directive to mean that Moses was to illustrate the legislation to the people by employing parables and other homiletical material to make these laws appear acceptable in their eyes. As a result of clever presentation of all these laws the people would be prepared to swear an oath obligating themselves to observe all of these commandments. The statement in Shabbat 86 that the Israelites did not say: "we will listen and do," but: "we will do and listen," was the outcome of their each having been "crowned" by 600,000 angels. All these comments prove that our paragraph refers to events prior to the giving of the Torah.