“I thought Jesus laid it out pretty clear - the tribulation starts with the destruction of the temple and city - and then ends with his coming.”
It has to do with attempts to link the chronology of Revelation with the chronology of Daniel’s 70th “week”. Since that passage in Daniel describes a 7 year period which is divided into two 3 1/2 year periods at the midpoint, and Revelation describes several periods of days that are roughly 3 1/2 years as well, some people want to try and interpret one prophecy in light of the other to construct a timeline, and that of course leads to having to account for the whole 7 year period that Daniel talks about.
Seventy weeks was determined to scatter the power of the holy people
Jesus was crusafide in the middle of the week, about three and one half
years later Steven was killed the result being that many believers left
and went to places such as Antioch and started preaching the gospel
therefore full filling danials 70 weeks, makes sense to me but I don’t know.