And the reason why the loading times are pretty quick is because he is on PC
Not to detract from the speed of the run itself, which is very awesome, but the "loading" screen can be easily edited out of the video, y'know. I play on a pretty high end PC and while loading times are short, I still see the spinning circle for 2-3 seconds. Some of those loading transitions are
immediate, which to me says "edited out." I've done it myself on some of my vids cause I figure no one wants to repeatedly look at the loading circle.

(edit: in part3 at 8:36 he missed one, hehe)
PS I'm also fairly convinced they sped up the run speed of their character by a small bit...default run speed doesn't produce that kind of fly-by on my screen, but increase run speed by .10 or .20 does. This wouldn't affect overall time by much or anything tho.