You say that the beast described in Revelation 13:1-10 appears at the beginning of the 3.5-year period. But can you give any explanation for the other beast described in Revelation 13:11-17, because this beast has no place within this 3.5 year period?
To be sincere, I am surprised by the question, for it is very clear from this chapter that the second beast, which is described in Revelation 13:11-17, will work in the period of the Antichrist, and it is he that makes all the inhabitants of the earth worship the Antichrist. He will convince the inhabitants of the earth to make an image to the Antichrist (Revelation 13:14), he will cause all the inhabitants of the earth to be given a mark on their right hand or on their forehead, and he will provide that no one will be able to buy or to sell, except the one who has the mark, either the name of the beast or the number of his name. (Revelation 13:16-17).
Then I saw another beast coming up out of the earth; and he had two horns like a lamb and he spoke as a dragon. He exercises all the authority of the first beast in his presence. And he makes the earth and those who dwell in it to worship the first beast, whose fatal wound was healed. He performs great signs, so that he even makes fire come down out of heaven to the earth in the presence of men. And he deceives those who dwell on the earth because of the signs which it was given him to perform in the presence of the beast, telling those who dwell on the earth to make an image to the beast who had the wound of the sword and has come to life. And it was given to him to give breath to the image of the beast, so that the image of the beast would even speak and cause as many as do not worship the image of the beast to be killed. And he causes all, the small and the great, and the rich and the poor, and the free men and the slaves, to be given a mark on their right hand or on their forehead, and he provides that no one will be able to buy or to sell, except the one who has the mark, either the name of the beast or the number of his name. (Revelation 13:11-17)
In Revelation 19, we find that this beast, which made all the inhabitants of the earth worship the first beast and his image and receive the mark of the beast (in this text he is called the false prophet) is seized with the first beast, that is, the Antichrist, and both are thrown alive into the lake of fire which burns with brimstone, thereby showing that they will end their activity at the same time:
And I saw the beast and the kings of the earth and their armies assembled to make war against Him who sat on the horse and against His army. And the beast was seized, and with him the false prophet who performed the signs in his presence, by which he deceived those who had received the mark of the beast and those who worshiped his image; ; these two were thrown alive into the lake of fire which burns with brimstone. (Revelation 19:19-20)
For deeper knowledge of the subject, I recommend that you study the course of Revelation in four parts.
Translated by Marcela Tașca