Can people be saved during the tribulation?
The short answer is “yes,” because of God’s merciful character. The good news is, our God is a God who is not willing for any to perish but desires all to reach repentance (2 Peter 3:9-13), so you can bet He will do everything possible to allow people as much time as possible to come to Him. In fact, that passage referenced here teaches us that God has only waited to judge the world because He wants more people to get the chance to come to Him, and He is calling us as the church in that passage to help hasten His coming by calling more people to reconcile with Him.
The Bible shows us that God is willing to save even during the tribulation period described in the book of Revelation when God is pouring out judgments on the earth. Before Jesus returns for good to defeat all evil, He calls His people up to join Him in the air (1 Thessalonians 4:17), what people often call the “rapture.” After that, believers are gone from the earth for the time being, but people still living on earth do appear to get a chance to repent and believe after the rapture. People who did not get called up to join Jesus clearly were not true followers of Him, but there are true followers of Jesus spoken about during the tribulation period after the rapture in the book of Revelation—those who are killed for not taking the mark of the beast (Revelation 13:7-10, 20:4), which shows us that some people do come to saving knowledge of God after the rapture.
Once Jesus does return the final time, the Bible is clear that He comes for judgment at that time (Revelation 19), and everyone who has not chosen to hide in His body on the cross by faith will face the judgment of God for their sins and will be killed. All have the chance now to be covered in Jesus and to hide in Him so they can escape that judgment, but we must encourage and persuade them to choose Him now before it’s too late. For those who think they know Jesus but are not confident, it is critical that they heed the many Bible passages encouraging them to test themselves to see whether they are in the faith.