https://www.gamespot.com/articles/destiny-2-servers-down-for-maintenance-offline-tim/1100-6453562/

Destiny 2 players looking to get stuck into some shootin' and lootin' today may want to keep in mind that servers for Bungie's popular shooter will be going offline for maintenance. The downtime is scheduled to begin at 6 AM PT / 2 PM BST / 11 PM AEST on September 25, and players won't be able to sign in to the game from that point. [Update: Servers are now offline and will not return as soon as expected. Bungie announced on Twitter that the maintenance period has been extended until 2 PM PT.]

An hour later, anyone that is already logged in to Destiny 2 will be kicked off, so plan your in-game activities accordingly; you don't want to get the boot while in a raid. Servers will undergo maintenance for a total of six hours.