Duran, if you can present me a scripture that says the GT is 42 months, I'll believe. The scripture you are referring to, says nothing of the sort. Note what it says: "And a mouth speaking great things and blasphemies was given it, and authority to act forty-two months was given it." (Rev. 13:5 NW) Nothing about the GT there. And that the GT might be cut short, is clearly stated at Matt. 24:22; Mark 13:20.
Where do I get my 7 years from? Mainly from the book of Daniel as I'll demonstrate. It's quite a mouthful. Each segment on its own might be lacking coherence and seem unconvincing, but as a whole the different aspects do contribute to a complete picture.
First clue: God works in heptads, i.e., sevens. E.g., creative days. 3 ½, half of that, means unfinished business.
Second clue: The outer courtyard of the temple sanctuary, a part of the Israel of God, is to be trampled by the nations for 42 months. IMO this will happen during the second half of the GT. See later. (Gal. 6:15, 16; Rev. 11:2; cf. Dan. 7:25; 12:7; 1 Cor. 3:16, 17; 2 Cor. 1:21, 22; Eph. 2:21, 22).
Third clue: Daniel’s time, times and half a time, which is 3 ½ years. Daniel’s “time, and times and half a time” covers the second half of the Tribulation because at the end of it the eleventh horn, having plucked up three horns, is destroyed at Armageddon (Daniel 7:8, 21, 25; cf. 12:7).
The two prophets will be prophesying for 1,260 days. Their public ministry will start immediately after the sixth trumpet blast (Rev. 9:13; 11:3). 1,260 days will then overlap with the 42 months of trampling, which starts in the middle of the Tribulation period. They will be announcing the 10 plagues, which will be starting during the 6th trumpet blast (Rev. 9:18, 20; 15&16).
Fourth clue: Second half of Tribulation is 1,260 days. Daniel 8. Vision of the 2,300 evening-mornings. To cut a long story short. Evening-morning: 1) The two nouns are singular. 2) Lit. an “evening-morning” time unit (not time, year or day), resulting in a most unusual time scale. 3) Evening in Hebrew means when the sun goes down. Morning means first light, when the sun comes up, until midday when the sun is at its zenith. Afternoon, when the day starts to fade, is not part of the equation. 4) One evening-morning is therefore 18/24 hours = ¾ of a day. 2300 evening-morning x ¾ = 1725 days. This literal interpretation does not deviate from Hebrew usage (Ex. 12:6, 10; 16:8-13; 27:21a; cf. 1 Kings 17:6).
I view the trumpet blasts and plagues as the GT proper. That means 7 trumpet blasts x 180 days = 1,260 days. Same goes for the vials of plague, 7 vials x 180 days = 1,260 days. The calculation therefore works as follows: 360 days + 1,260 days + 105 days = 1,725 days, i.e., 6th and 7th trumpet blast + second half of GT + Day of the LORD = 1,725 days.
Fifth and final clue: Dan. 12:11, 12
The final chapter of Daniel should be seen within the context of the Great Tribulation, this from the vantage of the victorious King of the North (cf. Dan. 11:40-44; 12:1, 4, 7, 10). The sum of the two periods of Dan. 12:11, 12 is longer than a Heptad. As seen, a Heptad is 7 years or 2,520 days long. 1,290 days + 1,335 days = 2,625 days. 2,625 days – 2,520 days of the Great Tribulation = 105 days. This is the equivalent of 3½ months (the end of the Tribulation to Armageddon, the closing chapter called the LORD’s Day). See Zech 14:1, 6, 7. According to this reckoning the beast will become king on day 1,290. I see its reign to be less than 1,335 days, during which it will be destroyed (cf. Rev. 17:8, 11).
Duran, there will be a repetition of celestial events: Seal 6: Rev. 6:12-17. Fourth trumpet blast: 8:12. During Jesus' Second Coming: Matt. 24:29. Armageddon: Zech. 14:6, 7.