Many of those who are sleeping in the ground will awake to life eternal (vv. 2a, 13a; John 5:28-29a; 1 Thes. 4:16). The sleeping saints will rise up to be resurrected to the air to meet with Christ.
The vision in Daniel 12 also covers things in the kingdom age.
After the resurrection, the kingdom of God and of Christ will become the eternal kingdom, as signified by the great mountain (Dan. 2:35), thus ushering in the kingdom age. With the coming of the kingdom, there will be the cleansing and recovering of the defiled and trampled temple for thirty days (12:11). This will continue the last one thousand two hundred sixty days (Rev. 12:6) as the end of the previous age to make it one thousand two hundred ninety days. Just as the Maccabees cleansed the temple after it had been defiled by Antiochus Epiphanes, so the saved Jews will cleanse the temple at the beginning of the millennial kingdom.
Daniel 12:12 says, "Blessed is he who waits and reaches the thousand three hundred and thirty-five days." With the beginning of the kingdom age, there will also be the preparing and reestablishing of the priesthood for the offering of the daily sacrifice to God for forty-five days, which will continue the one thousand two hundred ninety days to be the one thousand three hundred thirty-five days. Such an offering of the daily sacrifice to God will be a blessing to the chosen people of God (v. 12a; Joel 2:14). Forty-five days will be needed to recover the destroyed system of the worship of God with the sacrifices. The restoration of the sacrifices will be a great blessing to the people of Israel.