"Ellen White wrote about how after Satan appears there will be 42 months.."

Ellen White suggesting there would be "42 months" AFTER Satan appears, as in a future appearance, does not fit with my study of prophecy. I haven't seen such a statement that could be positively identified as her saying that, but I would not be surprised that some statement she made might lead others to interpret it in that way.

I'll cautiously check out the film you mentioned, sounds interesting...

Other Manuscripts Volume Nineteen (1902)

In the last days Satan will appear as an angel of light, with
great power and heavenly glory, and claim to be the Lord of the whole
earth. He will declare that the Sabbath has been changed from the
seventh to the first day of the week; and as lord of the first day of
the week he will present this spurious sabbath as a test of loyalty to
him. Then will take place the final fulfillment of the Revelator's
prophecy. [ Rev. 13:4-18, quoted.]

In connection with this scripture, the entire fourteenth chapter
of Revelation should be studied much by God's people. Verses nine to
eleven bring to view the special message of warning against worshiping
the beast and his image, and receiving his mark in the forehead or in
the hand. This warning is to be given to the world by those who are
mentioned in the twelfth verse as keeping "the commandments of God, and
the faith of Jesus." 

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Rev 13:4 And they worshipped the dragon which gave power unto the beast: and they worshipped the beast, saying, Who is like unto the beast? who is able to make war with him?
Rev 13:5 And there was given unto him a mouth speaking great things and blasphemies; and power was given unto him to continue forty and two months.
Rev 13:6 And he opened his mouth in blasphemy against God, to blaspheme his name, and his tabernacle, and them that dwell in heaven.
Rev 13:7 And it was given unto him to make war with the saints, and to overcome them: and power was given him over all kindreds, and tongues, and nations.
Rev 13:8 And all that dwell upon the earth shall worship him, whose names are not written in the book of life of the Lamb slain from the foundation of the world.
Rev 13:9 If any man have an ear, let him hear.
Rev 13:10 He that leadeth into captivity shall go into captivity: he that killeth with the sword must be killed with the sword. Here is the patience and the faith of the saints.
Rev 13:11 And I beheld another beast coming up out of the earth; and he had two horns like a lamb, and he spake as a dragon.
Rev 13:12 And he exerciseth all the power of the first beast before him, and causeth the earth and them which dwell therein to worship the first beast, whose deadly wound was healed.
Rev 13:13 And he doeth great wonders, so that he maketh fire come down from heaven on the earth in the sight of men,
Rev 13:14 And deceiveth them that dwell on the earth by the means of those miracles which he had power to do in the sight of the beast; saying to them that dwell on the earth, that they should make an image to the beast, which had the wound by a sword, and did live.
Rev 13:15 And he had power to give life unto the image of the beast, that the image of the beast should both speak, and cause that as many as would not worship the image of the beast should be killed.
Rev 13:16 And he causeth all, both small and great, rich and poor, free and bond, to receive a mark in their right hand, or in their foreheads:
Rev 13:17 And that no man might buy or sell, save he that had the mark, or the name of the beast, or the number of his name.
Rev 13:18 Here is wisdom. Let him that hath understanding count the number of the beast: for it is the number of a man; and his number is Six hundred threescore and six.
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42 months are definitely going to come in the future according to this writing.