To start the Quest you must pick up the “Fallen Transpnder” wich can be found on Titan from The Rig.
If you cannot access this room, make sure you have completed the campaign & Rat King quest (Enemy of my enemy) on Titan. The door will not open if you have not completed the world quest “Enemy of my Enemy“.
After you have finished all the Node Data Locations you have to go to the farm, talk to the Fallen hiding in the basement. This starts the mission.
In the video below you can see all the steps you need to do, including timestamps.
Note Data Locations Outbreak Perfected Mission “Zero Hour”
00:00 – Fallen Transponder from Titan: The Rig
01:16 – 6 Nodes from Lost Sectors
01:24 – EDZ: Widow’s Walk – Node Data Location
02:05 – EDZ: Atrium – Node Data Location
02:45 – EDZ: The Drain – Node Data Location
03:35 – EDZ: Whispered Falls – Node Data Location
04:09 – Nessus: The Rift – Node Data Location
05:09 – Nessus: The Carrion Pit – Node Data Location