Fastest speedrun was like not even 10 minutes.

And that was to beat him. Just reaching him and dying to him should go substantially faster:

• get levitation potions/scrolls
• grab Icarian Flight
• have some form of suped speed enhancement (cumulative potions, Boots of Blinding Speed etc.)
• carefully aim north of Ghost Gate and hop
• rush through Dagoth Ur (location) into Facility Chamber
• whack ol' Three Eyes and have him demolish you