I just did Temporal Sanctum to exalt slam my Dragonsong, and tried to interact with the Eternity Cache, but couldn’t and freaked out and didn’t realize I needed to press the swap era button.
How dumb am I? 
I’m sad, and no keys left. 
Yeah. That’s where I freaked out. 
I had a whole different foolish idea of how this works. I thought you had to put the LP item along with the exalted to get the stat you want and then revisit the exact same spot but in a different timeline and not in the dungeon. Felt a total dumbhead when i saw that right after you change eras in the dungeon i could just retrieve my item instantly.
Btw i had an item stashed there for 3 dungeon runs because i was visiting the altar in the exact same era and I was feeling annoyed every.single.time…
Well, if you’re dumb, then I’m dumb as well. Same thing happened to me the first time.
Fortunately I had plenty of keys because of key-drop nodes I selected in the Weaver tree.