Hello YehovaYeshua,
First of all, your error here is the assumption that the gathering of the church immediately initiates the seven years, which it does not. Sometime after the church has been caught up, that ruler, the antichrist will establish his seven year covenant with Israel(Dan.9:27) and that is what initiates the seven years.
And secondly, it is your claim of "we would be able to calculate the exact date of Jesus's return" is correct and is one of the features which separates the appearing of the Lord to gather the church vs. the Lord's return to the earth to end the age. The gathering of the church is and has always been imminent. Believers are to continue to be watching and ready for the Lord's return because He will come like a thief in the night.
In opposition, prior to the Lord's return to the earth to end the age, the church must be gathered, the seven year covenant with Israel must be established, the wrath of God via the seals, trumpets and bowl judgments must take place. And then shortly after the seventh bowl has been poured out, then the Lord will return.
The bottom line is that regarding the Lord's return to the earth to end the age, there are all kinds of signs that must take place which will allow believers on the earth during that time to know the approximate time by reading along in Revelation by counting off each seal, trumpet and bowl judgment. When the seventh angel pours out his bowl, the greatest earthquake to ever hit the earth since mankind has been on it will take place, causing the mountains and islands to disappear. The cities of the nations will collapse and there will be a great hail storm with hail weighing from 75 to 100 lbs. Once a person sees that event take place, then the sun and moon will be darkened and the stars (meteorites/asteroids) will fall to the earth and the inhabitants of the earth will see the Son of Man arriving on the clouds of heaven with great glory and will send out His angels to first gather the weeds and then the wheat.