Albert Barnes Commentary Exodus 40:17

"And it came to pass in the first month in the second year, on the first day of the month, that the tabernacle was reared up." — Exodus 40:17 (ASV)

On the first day of the month - That is, on the first of the month Nisan (Exodus 12:2; Exodus 13:4), one year, lacking fourteen days, after the departure of the Israelites from Egypt. They had been nearly three months in reaching the foot of Mount Sinai (Exodus 19:1); Moses had spent eighty days on the mountain (Exodus 24:18; Exodus 34:28), and some time must be allowed for what is related in (Exodus 24:0), as well as for the interval between the two periods which Moses spent on the mountain (Exodus 33:1–23). The construction of the tabernacle and its furniture would thus appear to have occupied something less than half a year.