The "extra 30 days" lies before the midpoint of Daniel's 70th week, not after the completion of the 70th week. From Daniel 12:17 we read "From the time that the regular sacrifice is abolished and the abomination of desolation is set up, there will be 1,290 days. So we have 30 days before the midpoint + the 1260 days (3 1/2 years) consisting of the second half of the 70th week. Here's how it happens:
The Antichrist declares himself to be God 30 days before midpoint of the 70th week (Daniel 12:17).
When those who are in Jerusalem see this they are to immediately flee to the mountains just as Jesus warned in Matthew 17:16. Some theologians call this the "flight phase" of Daniel's 70th week because it is during this 30 days that the Jews are fleeing from the antichrist.
At the exact midpoint of the 70th week the Jews who are fleeing are supernaturally transported to the wilderness refuge where they are supernaturally protected for 3 1/2 years. Read it for yourself in Revelation 12:6 and12:14.
What happens to these Jews at the end of the 3 1/2 years? Well, they are released by Jesus Christ from the wilderness refuge because they have finally recognized Him whom they have pierced (Zechariah 12:10). Once released, they begin their jubilant march to Zion (Hos 2:14, Is 35:1-10) .
But Jesus still has work to do. He goes to the aid of those in Judea who did not heed Jesus' warning to flee. One there, he engages and defeats the antichrist at the battle of Armageddon. That is why it is written in Daniel 12:12 "How blessed is he who keeps waiting and attains to the 1,335 days!" (45 days after the completion of the 70th week).
And why is the person blessed who attains to the 1,335 days? Here is the reason: "But when the Son of Man comes in his Glory, and all the angels with Him, then He will sit on His glorious throne. All the nations will be gathered before Him; and He will separate them from one another, as the shepherd separates the sheep from the goats;" Matthew 25:31
Clear and Simple