Opening Cerimony on August 6th
It will be available for the entire release.
Source: https://forum-en.gw2archive.eu/forum/livingworld/jubilee/The-Opening-Ceremony
It will most likely be a personal instance thing like the Bazaar had. You run up to the green star and watch a cut scene, then maybe you do quick instance with whoever is involved.
EDIT: from a dev – More along the lines of Braham/Rox and it’s available for the entire release.