Tracking the 18h CD on the ability to instantly complete a world quest would make alt hopping a lot less frequent.

The order hall upgrade is available to Warlocks, Mages, Demon Hunters, Death knights Warriors and Paladins.

To make them show up under the "Daily Quests" list, add to "local _specialQuests":

[44209] = { zid=1014, daily=true, sid=221602 }, -- Mage: Might of Dalaran
[44227] = { zid=1014, daily=true, sid=219540 }, -- Warlock: Unleash Infernal
[44224] = { zid=1014, daily=true, sid=221561 }, -- Demon Hunter: Rift Cannon
[44222] = { zid=1014, daily=true, sid=221597 }, -- Warrior: Call the Val'kyr
[44234] = { zid=1014, daily=true, sid=221557 }, -- Death Knight: Summon Frost Wyrm
[44220] = { zid=1014, daily=true, sid=221587 }, -- Paladin: Vanguard of the Silver Hand

The quest ID that I used above is the "tutorial" quest you get after first researching that wants you to use the ability.

I did get lazy and put the zone as Dalaran (1014) for all of them, where you could argue the order hall zones makes more sense.

I would have preferred to display them as a separate line with a check box for uses, but that is far more complex in the code so the above was sufficient for my needs.

It appears the addon is still not tracking this, or am I mistaken? I can't see anything in the code, nor does it show ingame.

The easiest way is to simply track the spell's cooldown via GetSpellCooldown() API.

Credit for picking up the item to do the 18h ability with:
WQ Nuke Quest Item Collected.

I went here to request the same notifier.

If it is any help, the order hall advancement 18H names are:

Death Knight: Frost Wyrm
Warlock: Unleash Infernal
Warrior: Val'kyr Call
Demon Hunter: Fel Hammer's Wrath
Mage: Might of Dalaran
Paladin: Grand Crusade

This page is related to being creditted the first use, no idea if it can help track down the timer:
Use the World Quest Nuke spell. Internal Only

Well, seeing how Blizzard removed the ability we might as well close this.