that's generally how long the fight took total tamoa, the dnc you came across was probably not geared properly, not using food, or no cuor buffs/atma. see the time stamp on my buffs, i was in zone for a total of 11ish minutes, and i wasted roughly 4 minutes of that getting there, building tp, and agro/pulling it.
Don't think it's soloable for dnc due to the -DT. I came across a dnc trying to solo it before, it was @ 76% and the guy had been fighting for 40ish mins. He invited me and my Bliz3 (with atmas and maatk temp item) did around 150 dmg, went downhill from there. Ended up with nukes that did less than 20 dmg.