Whatever power Satan has, he cannot touch those that are Christ's own except as the Lord may permit a shaking for disciplinary purposes with a good end in view. The Lord Jesus said to Peter: "31* And the Lord said, Simon, Simon, behold, Satan hath desired to have you, that he may sift you as wheat:
32* But I have prayed for thee, that thy faith fail not: and when thou art converted, strengthen thy brethren." (Luke 22:31, 32).
Also, Job was tried to show Satan that he did love the Lord not for any blessings Job got from God, but for His own sake. (Job chapters 1, 2).
As to the Tribulation, it will last seven years, this has to do with prophetic studies, and if you want to PM me I can give you bibliography on that, but for it to begin the Man of Sin has to be revealed. And it has to do with the judgment of the world. God's children have not been appointed to wrath, but to salvation. Satan will indeed work havoc on the world, but only as allowed by God in His judgmental purposes against a world that has been and is rejecting Christ Jesus.
At the very end of the Gospel of Matthew it says: "And behold, I am with you all the days, until the completion of the age." (New Translation.)
doulos