Dilated Eon Canister is a binds-when-picked currency tied to the Time Rifts in World of Warcraft Dragonflight Season Four.
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Unlike Dreamsurge Cradle, which is tied to the Dreamsurge event, Dilated Eon Canister doesn't specify what it's for. So, what should you do with Dilated Eon Canister in Dragonflight?
Currently, Dilated Eon Canister has no known uses in Dragonflight. It drops from Awakened Time Rifts. Unfortunately, Time Rift vendors in Tyrhold Reservoir do not sell items, toys, transmogs, or gear. The vendors are still in their usual spots, at coordinates 51, 56 in Thaldraszus, but if you try to interact with them, they simply ignore you and go about their day.
I suspect this is a bug, like Dreamsurge Cradle, and a fix is coming. This was likely an oversight by Blizzard Entertainment, as all open world events on the Dragon Isles were updated with season four. All events now have better rewards that will get you and your alts up to speed in no time.