The Invasion Dungeon can be accessed after you complete the main quest "How to Hide the Truth".
The Invasion occurs daily in two of the Hard Difficulty Infiltration Operations. You can enter the same Invasion twice per day.
Earn additional rewards from the Invasion when completing it within the time limit.
To view the reward info for each section, hover over the trophy icon for that section in the Tooltip.
Enter Invasions through the Map (G) or Albion > Infiltration Operations Terminal.