The subject of this article or section is part of WoW's Anniversary, a seasonal event that typically lasts two weeks. Once the event has run its course, this will no longer be available until next year, but there are no guarantees.
The chronocrystals are all lined up chronologically.
Chronocrystals are devices utilized by the Keepers of Time in the Caverns of Time. They allow adventurers a chance to view certain past events once more.