In October 2016, the CBR website published another in their long line of articles dealing with comic legends, this one titled ““Zero Hour” was originally going to end with the Justice Society of America on their own separate Earth.”
You can read the full article here (scroll down past the Silver Surfer story) but this quote from writer Dan Jurgens sums it up:
What would have happened if the Hal Jordan/ Parallax character create other Earths, I wanted one Earth to survive to put the JSA on, and give them back Earth-2. If you had that separation, they would always have a place to be where time could exist on its own, and they could exist with the DC Universe.
Here’s a short page with what I’ve found.