Chromie Time is a new feature introduced in World of Warcraft: Shadowlands which allows level 10 players to choose their path of adventure (the expansion) to level up from level 10-50.
Alliance players should go to the Stormwind Embassy (through the Dwarven District).
Horde players should go to the Orgrimmar Embassy.
When you talk to Chromie, you must select a different timeline.
Then you will see several choices: Kalimdor and Eastern Kingdoms (Catalysm), Outland (Burning Crusade), Northrend (Wrath of the Lich King), Pandaria (Mists of Pandaria), Draenor (Warlords of Draenor), or Broken Isles (Legion).