Gabriel tells Daniel: “There are seventy weeks that have been determined upon your people and upon your holy city, in order to terminate the transgression, and to finish off sin, and to make atonement for error, and to bring in righteousness for times indefinite, and to imprint a seal upon vision and prophet, and to anoint the Holy of Holies.

Daniel 9:24,

This would occur within “seventy weeks.” Since Gabriel does not mention days, these are not weeks of seven days each, which would amount to 490 days—a mere year and a third. The foretold rebuilding of Jerusalem “with a public square and moat” took much longer than that. The weeks are weeks of years. That each week is seven years long is suggested by a number of modern translations. For example, “seventy weeks of years” is a rendering indicated by a footnote on Daniel 9:24 in Tanakh—The Holy Scriptures, published by The Jewish Publication Society. An American Translation reads: “Seventy weeks of years are destined for your people and for your holy city.” Similar renderings appear in the translations by Moffatt and Rotherham.

Interestingly, The Revised English Bible reads: “Seventy times seven years are marked out for your people and your holy city.” Following their exile and suffering in Babylon for 70 years, the Jews would experience special favor from God for 490 years, or 70 years multiplied by 7.