Okay, I had a chance to test this as I had a level 59 just ding 60. He had even already been in the Dragon Isles.
The choices are there, but like that forum post said, you have to go through her dialogue options. In the dropdown below are the screenshots of my conversation with Chromie.
CLICK FOR SCREENSHOTS
Just dinged 60
Talk to Chromie and select her dialogue option.
Choose “What are timewalking campaigns”
Choose “What timeline should I choose”
Here is the list of which dialogue choice corresponds to which timeline.
I chose Cataclysm and the next dialogue option is the request to be put in that timeline.
You are now given the corresponding quest that takes you to the Warboard.
Click on warboard and then Chromie will be next to it to complete the quest.
Turn in the quest to her.
As you can see, I now have the appropriate dungeons for my timeline.
