I don't see how the 3rd day of the 3rd month of Sivan when the Lord descended upon Mt. Sinai could be the same day as Sivan 6 because Sivan 6 would be the 6th day of the month of Sivan although Moses must have been up on Mt. Sinai on Sivan 6 because he was up there for 40 days and forty nights according to Exodus 24:18. The Bible doesn't say what day of the month the Lord gave Moses the 10 commandments on the tables of stone although the Jewish people claim it was on Sivan 6 which is the same day that the Jewish people celebrate the Feast of Weeks also called the Feast of Shavout (Pentecost.) If Moses went up the mountain the 3rd day of the 3rd month of Sivan by himself the first time, I assume it must have been the 4th or 5th day that he took his brother Aaron, the priest up along with Aaron's two sons Nadab and Abihu and the 70 elders (Exodus 24:1 & 9 up the mountain to see the Lord. Then Moses goes up the mountain one more time (Exodus 24:12-18) and the Lord gives him the ten commandments on the tables of stone.