No Magic number brother........... 3 1/2 years or seven years depending on who you ask.
I am not going through all the scriptures where those number are given.
3 1/2 years many speculate would not be long enough for the Antichrist to set up, they start the tribulation as a seven year period, 3 1/2 years into the Tribulation the Antichrist sits in Israel calling himself God.
After that many refer to the last 3 1/2 years as the Great Tribulation.
Either way it's a definite defined period God gave to accomplish what He intends to do, and Jesus said those days are shortened, meaning they have a specific time frame.
All I can do is prove two cases of seven years or 3 1/2 years but seven is the start of something and completion of it.
Jesus Is Lord.
and theres absolutely no way to prove that 3 1/2 years or any other number is correct.
these kinda things are usually speculation that cannot be proven.