Mythic Keystones are special items that allow a player to begin a Mythic+ dungeon. The tooltip for these Keystones lists important information:
The dungeon for which the Keystone is attuned
The level of the Keystone
Any affixes that might be in play for that dungeon (see below)
The remaining duration on the Keystone item, which expires on the weekly dungeon lockout
A player may only possess one Mythic Keystone at a time, and will only receive one keystone per week. Even if you delete your current Keystone, you will not receive a new one from any of the possible Keystone sources until the dungeon/raid week has passed. Do not delete Keystones – though note that, if you do accidentally delete your Keystone, you can recover it through the battle.net Item Restoration service.
The following table represents the timers for the various rewards in Mythic+ dungeons: