28 “And the world will be as it was in the days of Lot. People went about their daily business—eating and drinking, buying and selling, farming and building-- 29 until the morning Lot left Sodom. Then fire and burning sulfur rained down from heaven and destroyed them all. 30 Yes, it will be ‘business as usual’ right up to the day when the Son of Man is revealed. 31 On that day a person out on the deck of a roof must not go down into the house to pack. A person out in the field must not return home. 32 Remember what happened to Lot’s wife! 33 If you cling to your life, you will lose it, and if you let your life go, you will save it. 34 That night two people will be asleep in one bed; one will be taken, the other left. 35 Two women will be grinding flour together at the mill; one will be taken, the other left.”
37 “Where will this happen, Lord?” the disciples asked.
Jesus replied, “Just as the gathering of vultures shows there is a carcass nearby, so these signs indicate that the end is near.” (Luke 17:26-37 NLT)
When will Jesus return. The answer is we don't know exactly when. We do know Jesus' return will be when people least expect it. He tells us to always be reading by living in faith and being faithful to Him. Don't worry about being left behind. God promises that nothing can separate us from His love for us in Jesus Christ.
Some of the warnings Jesus gave were to prepare His followers for the destruction of the temple in Jerusalem in 70 AD by Titus and the Romans. Christians paid attention to the warnings and fled Jerusalem before it happened. People who do not understand this have created what I believe to be incorrect understanding of Jesus' return. Jesus never said that people left behind after His return will be given a second chance. He tells us to watch and pray for His return.