God told them
He was their Savior, many times, not the Law, not the blood of bulls and goats. They also knew of the Plan of Salvation from Abraham, so they did know that a Savior was coming to earth, ie,
the time of their visitation. They just refused to believe God and believe the time, which Daniel foretold for them, as did the other prophets. They didn't want to hear it. In fact, they often killed the messenger
Everyone who has heard the Good News of Jesus Christ and the Plan of Salvation and refuses to believe it, is without excuse.
Since God, and God alone, has always been the only Savior, I for one, can't see these "two dispensations".
They also knew of the Plan of Salvation from Abraham, so they did know that a Savior was coming to earth, ie, the time of their visitation. But their expectation was that the Messiah would set up a physical, political, religious Kingdom on earth that all nations would look to. They had no idea that the Messiah was coming to set up a spiritual Kingdom. The Gospel was even hid from the Apostles. It was only revealed after the Cross.
Luke 18:31-34