While you have Timeless Conflict allocated on your Atlas Skill Tree, breaking out monsters and chests from stasis will contribute progress towards a Schism, as shown by a progress bar. Once the progress bar is full, the Schism will occur and the Legion encounter will begin. Breaking out monsters and chests with rewards or more powerful monsters will contribute more progress towards the Schism.
Timeless Conflict is a new Atlas Keystone in PoE 3.22.