Hebrews 12 teaches a first century “covenant-transition. As the Old Covenant was being removed, the New Covenant was being fully established. Meaning, that the New Covenant could not be fully established until the Old Covenant was fully taken away. But, Hebrews 12 also teaches that at the full removal of the Old Covenant, the saints would receive the Kingdom of God. Said another way, the full establishment of the New Covenant would mean that the Kingdom of God had fully arrived and had been fully received. This took place in the first century through the destruction of Jerusalem in AD70. The chart below demonstrates this.
The Institute Of Fulfilled Eschatology