I used 6 chars on the talon farming which I had placed in each zone but Tanaan as it doesn’t spawn there. Then I made a route with the Routes addon based on the coords on the spawn points in each zone as well. A list of spawn points for TomTom can be found on wowhead.
I read the topic about the void talon on wowhead very close. Some says it spawns randomly in each zone within a 12 hour window. Other says the portal has guaranteed spawn within a 3 hour window in any zone. Someone also says he saw the portal twice on 2 different locations within 10-15 mins.
A little confusing…
Anyway. I decided to go for the 3 hour window solution and spend 3 hours on farming the talon portal in all zones. I logged each char and flew each route without any breaks. The portal popped after 25-30 mins. At that time I guess my total farm time was accumulated around 5-6 hours.
The Routes addon makes it easier to fly and check each possible spawn point. It’s possible to do a complete check in all zones in 8-12 minutes. And if I remember correctly the portal is up for 10-15 mins. So a full check of all zones should reveal the portal sooner or later (unless someone else finds it before you).
btw. I also have the Chincilla minimap addon installed. I unlocked the minimap and dragged the it close to center/my char so it was easier for me to follow my route as it’s shown in the minimap as well.
The Routes addon can be quite awkward to learn. But once mastered it’s perfect for farming. I also used it for the Long-forgotten birdie in Aszuna.