Shoutouts to z32o for discovering this, and to Alanim, swinch, and Justin-credible for researching further.
Although very peculiar, it is possible to wrong warp in the Abyss section of Smithy's domain shortly after defeating Count Down, saving 7 seconds.
Specifically, the screen directly after the conveyor room that produces Machine Made Mack, which contains many conveyor belts & Boos. In order for the wrong warp to work, the order in which you do the Bowser's Keep doors, as well as what happens within them, matters.
The criteria for setting up the wrong warp are as follows:
Perform both sections that contain Dr. Topper (the quiz door & coin box door) before the Platform door first, if possible.*
Mario's Pad Manip guarantees this, and most frames of Nimbus Manip guarantee it as well. There are some outcomes of Nimbus Manip where this will not be possible.
3. When you reach the room in the Abyss containing the conveyor belts & Boos, simply hold up, fall off, get back on the trampoline, and you'll skip to the end of the screen. Do not step on the conveyor belts, simply hold straight up, otherwise the warp will not work.
(video credit: Justin-credible)
* NOTE: If you do the door containing the relay race last, it's possible to get lucky and still be able to perform the wrong warp anyways, even if you were unable to do the Platform door after the Topper doors. The coordinates of where the wrong warp will take you are dependent on how poorly the Goomba does in the relay race, with a worse position meaning the warp takes you further. Yes, this is real. Specifically...
Goomba in 1st: WW doesn't work
Goomba in 2nd: WW takes you halfway, breaking even with normal movement
Goomba in 3rd: WW takes you close to the end, saving ~5.5 seconds
Goomba in 4th: WW works properly, saving the full 7 seconds
So, keep all of this in mind while doing the Doors, so you can determine whether or not the wrong warp will work when you get to the Abyss.
Your cannonball direction, the Goomba's position, and your position within the conveyor room all share some variables, leading to this unexpected behaviour.
(Do not perform this warp in Most of the Stuff, it skips chests and your run will not be valid if you don't open them.)
z32o's original video where she discovered the warp