If you called into work this morning to play Destiny 2 all day, you're about to be super upset. Beginning at 9 a.m. ET the game will undergo a 6-hour maintenance period which means it'll be back up around 3 p.m. ET.
Bungie has not specified why they're taking the game down for that period, but the game is starting their "Faction Rally Event" tomorrow so it could be tied to that. As of writing, this is the third time since launch that the game's servers have gone offline for an extended period of time.
Hopefully, it happens less frequently going forward.