The Pretribulation rapture doctrine claims that Jesus comes to call out his church in a secret rapture and the church leaves the earth so God can continue with israel. In which time the world experiences a 7 year tribulation. 

However, some teach that if you are not ready and aren't watching when this time happens, or don't regard the rapture, God will punish you and leave you in tribulation. That isn't supported by scripture. If any of the pretribulation doctrine is even scriptural.

The dispensation doctrine says Daniel 9 leaves a gap between the 69th week (7 year periods) and the last week (7 years) sometimg into the future, in which will be tribulation to recall Israel. In the doctrine, Israel becoming a nation is the timepiece predicated on the whole theory. Israel becoming a nation starts a countdown of a generation, when Jesus said IN THIS GENERATION. They believe he was speaking of the generation in the future when it happens.

A biblical generation (even in our times) is 40 years. Osrael became a nation in 1948 counting down from then. The rapture would have to occut within 40 years brining us to 1988. However, 1988 passed without incident. Scholars began looking at 70 years as a generation, which actually is a lifetime. That brings us to 2018 without incident. Now the theory hangs on no timepiece so it is now a spiritual measure having no predicated timepiece. 

Every year scholars prdict the end times and prophets make declarations of the ripe time for a rapture. Each time it fails.