On the first day of the month - That is, on the first of the month Nisan Exodus 12:2; Exodus 13:4, one year, wanting 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, 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.
Related Commentaries of Exodus 40:17
Exodus 40:17
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.