As your comment of Luke 21 states,
It would seem to suggest that the nation of Israel would be destroyed and ruled by Gentiles.
So the Gentile times had not begun yet when Jesus was speaking.
Barbour & Russell's interpretation implies that they had begun over 6 centuries before. It's quite impossible IMO to derive such an idea from Luke 21. There the "Biblical patchwork" pops in, in effect distorting the Lukan text.
When I explained the Gentile times as a JW, I felt the need to paraphrase Luke as meaning "and Jerusalem will remain trodden by the nations". That's just not what the text says.
So, how "scriptural"?