If you take time to listen to the sermon in its entirity, David Wilkerson, did not prophesy a certain time. It is chilling sermon. The sermon is based on the book of ISAIAH.
In One Hour Everything is Going to Change, david Wilkerson
https://www.youtube.com/watch?v=8uUG4ZTy25s
In fact, he did not specify a city. Others have done that.