How long will the tribulation last for?

I am wanting to get opinions about how long the tribulation will be. To be more specific, I mean the "great tribulation" that is mentioned when talking about end time bible prophecy studies. I have read that the tribulation will be about 7 years in length, but also that it would only last for about 3 1/2 years according to other sources.

Are there other opinions about the length of the tribulation or has the tribulation already taken place?

The Bible describes a period of time referred to as "Daniel's 70th week" which is missing from "Daniel's 70 weeks". This time period is referred to as the tribulation period and lasts for a total of 7 years.

And he shall confirm the covenant with many for one week: and in the midst of the week he shall cause the sacrifice and the oblation to cease, and for the overspreading of abominations he shall make it desolate, even until the consummation, and that determined shall be poured upon the desolate.

Daniel 9:27

I believe the Bible clearly teaches us that the Great Tribulation will only last for seven years. If the tribulation will last more than seven years, the elect will not be saved because of the terrible things that could happen. Praise God for His compassion that it will only last for seven years.