Creatures with indestructible that enter the battlefield after Hour of Devastation resolves will still have indestructible.
Once Hour of Devastation begins to resolve, no player may take actions until it's done. Notably, players can't try to give a creature indestructible again to save it from the damage.
There are many important moments in the story, but the most crucial-called "story spotlights"-are shown on cards. You can read more about these events in the official Magic fiction at http://www.mtgstory.com.
Standard: Ej legal
EDH / Commander: Restricted
Pauper: Ej legal
Brawl: Ej legal
Historic: Ej legal
Premodern: Ej legal
93/94: Ej legal
Hour of Devastation är Legal i dessa block: Amonkhet