A Timely Summons from Shattrath

This quest is actually "A Timely Summons from Shattrath", available from [npc=111246] while Burning Crusade Timewalking is active. It is essentially a breadcrumb quest to Disturbance Detected: Black Temple, the Black Temple Timewalking quest.

Quest Text:
A Timely Summons from Shattrath
The blazing star holds a peculiar alignment this cycle, calling out across the heavens. Seek out the sage [npc=123252] in Shattrath City, and lend her your aid.
Quest Objectives
Meet with Vormu in Shattrath.
Rewards
You will receive: 1g94s

Note that if you join a group to run Black Temple Timewalking while you have this quest in your log you will be unable to turn it in and will have to abandon it in order to pick up Disturbance Detected: Black Temple. This quest is not flagged as a Raid quest, and therefore you cannot make any progress on it while in a raid group.

The portal for this quest is in the Chamber of the Guardian (in the center of Broken Isles Dalaran).
Go in and stand on the circle to be teleported to the other floor. Walk ahead and the portal you need is the 2nd on your left when you go down the stairs.

Blizz removed portals as of 8.1.5 so you will see an empty room. Go to your capital city and use the shattrath portal there.