This is also helpful: How to Build A Space-Time Crystal https://www.technologyreview.com/s/428334/how-to-build-a-spa...
That article is from 2012 and quotes:
"If that’s the case, we ought to be reading the details about the first space-time crystal sometime in the days and weeks to come. "
Was there something non obvious they had to overcome that took the extra few years to produce these space-time crystals?
(I use the term non obvious as if this was not all way beyond my ken!)
In any event, they sure seem to have made a lot of progress in just a few years. I look forward to reading more about this, as well as listening to Neil deGrasse Tyson describe it in his infectiously enthusiastic way.