I needed to get to UC on a level 23 toon and when I initially spoke to Zidormi outside Brill, she had no conversation option for me.
After doing exhaustive research and getting different answers depending on the date I eventually:
- switched to BfA timeline with Chromie and started that expansion
- switched again to Shadowlands and started that expansion
- switched again to Dragonflight
I then went over to Brill and talked to Zidormi and she now had the “switch back to earlier time” option. I have no idea which of the above actions started her up but it certainly seemed to be a huge timewaster when it would have been just as simple to have the NPC give me the option as do other similar versions of her across the game.
I note that the Blizzard support article was of zero use.