Third time's the charm, I guess.
With the use of the cursor-outside-window trick, I could at times reach TAS-level speed of walking between rooms, and I utilized every trick and glitch I knew of. There are of course improvements to be made, but by this point, you'd have to be even more demented than me to even try. Especially since most of possible improvements would involve managing to right-click on tiny objects while Briggs is moving, and any small mistake is a potential run killer. I just don't have the patience for any more of this - not when the best I could potentially muster would be a couple of seconds less than the current time.
If you want some extra information on how to speedrun the game, you can find them in the Resources, as well as in this video guide I made: