Some people assume that is what the apostle Paul meant when he wrote: "As God's fellow workers we urge you not to receive God's grace in vain. For he says, 'In the time of my favor I heard you, and in the day of salvation I helped you.' I tell you, now is the time of God's favor, now is the day of salvation" (2 Corinthians 6:1-2 2 Corinthians 6:1-2  We then, as workers together with him, beseech you also that you receive not the grace of God in vain.
 (For he said, I have heard you in a time accepted, and in the day of salvation have I succored you: behold, now is the accepted time; behold, now is the day of salvation.)
American King James Version×, NIV).
Paul meant exactly what he said. But be sure to notice what Paul did not say. He did not say that today is the only day of salvation, nor was that his intent.
In the original Greek there is no modifier before the phrase "day of salvation" in this verse. Most translations have added the word the before day in an attempt to clarify Paul's words—but in so doing have inadvertently led many to misunderstand. The Darby Translation italicizes "the" here to indicate that it has been added. Other versions translate this phrase as "a day of salvation" (Green's Literal Translation, Living Oracles New Testament).
Still other versions inconsistently translate the same phrase as "a day of salvation" in the first part of the verse and "the day of salvation" in the latter part (American Standard Version, Bible in Basic English, Green's Literal Translation, Modern King James Version, New Revised Standard Version, Phillips Modern English).
For those in the Church in this age, now is their day of salvation. God is calling them now. Salvation is available today to anyone who is willing to repent. That is what Paul meant. The word "the" could even fit in this context—the day of salvation for those God is calling in this age is now.
But Paul neither said nor implied that salvation is available only in this age. The day of salvation for the rest of the world is yet future. Paul in no way meant to contradict the many passages in the Bible that show that the world at large will have an opportunity for salvation in ages yet to come.