https://www.polygon.com/2017/9/21/16348294/destiny-2-faction-rallies-start-time

If you’ve reached Level 20 in Destiny 2, you’ve probably found yourself wondering aloud, “What should I be doing now to get those sweet, sweet power levels?” Beginning next Tuesday, Sept. 26, at 2 a.m. PT you’ll be able to pledge yourself to one of three factions when the game’s Faction Rallies go live.

What that means, in specific terms, is you go to the Tower, talk to one of the three above faction leaders, and then do some activities, like “public events, explore Lost Sectors, complete strikes, clear the raid, or compete in the Crucible.” Do stuff, get faction tokens, exchange faction tokens for loot. It’s Destiny! You’ll have until 2 a.m. PT on Oct. 3 to collect those tokens and the winning faction will be announced at 10 a.m. PT.