In fairness, five and a half hours is about what it took for several prior encounters to be cleared in the original Destiny, so the speed of people pushing for first completion hasn’t changed all that much. You can check out a clip from the end and the official tweet celebrating the clear just below, but be warned that there are some spoilers included. (Seeing as it’s the end of the Leviathan raid, you probably expected that.)
Congratulations to Clan 'The Legend Himself' on being the World First to complete the Leviathan Raid.
— Bungie (@Bungie) September 13, 2017