Walking = 1.716s Speed Jump = 1.367s Time Saved = 0.349s
How To Perform
Jump on the 1st possible frame. So just mash Jump button and hope you get it. Or find a timing if you can.
Where Does This Work?
Thanks to わあい (Waai) for discovering 5 years later why this works. It seems that if you land and jump from a slope and then grab a ledge, upon jumping after climbing (with proper timing) you get a speed boost!
What If I Fail, Do I Lose Time?
Even if you fail the "Speed Jump" and just get a normal jump you will still save 0.049s compared to walking, so there's no reason not to go for it since you save time regardless.
Source
あき一つ's video: https://twitter.com/akitsu0822/status/1236657500176257026
わあい's tweet figuring out how it works: https://x.com/Nordanix_SSBM/status/1897663865065787579
I've been thinking the last couple of days of even more changes, albeit not too large ones. The biggest one is the removal of the 3DS version. Both me and Ico came up to the conclusion that it's too different, essential "a different game".
This is due to it being: 30FPS, 10 Less Stages, 5 Less