Where would I find the Scripture that refers to the end of the world happening after everyone has heard the Word of God?
It is a misquoted verse. Jesus is talking about the end of Jerusalem when he said, "And this gospel of the kingdom will be preached in all the world as a witness to all the nations, and then the end will come" (Matthew 24:14).
That did happen during the first century.
"Because of the hope laid up for you in heaven, of which you previously heard in the word of truth, the gospel which has come to you, just as in all the world also it is constantly bearing fruit and increasing, even as it has been doing in you also since the day you heard of it and understood the grace of God in truth" (Colossians 1:5-6).
"If indeed you continue in the faith, grounded and steadfast, and are not moved away from the hope of the gospel which you heard, which was preached to every creature under heaven, of which I, Paul, became a minister" (Colossians 1:23).
And Jerusalem fell in A.D. 70, after Colossians was written.