Out of curiousity I timed this exactly. When I write "x" frames off I mean this is as many frames you spend with NO input after being off of the wall and before holding right. For example 2 frames off means your inputs are right+a, no input, no input, b+left for those 4 frames.

Also it doesn't matter when you press b as long as it's on or before the frame you hold right, and after you jump.

Frames off --- Frames saved: 0 --- ?¤ 1 --- 3 2 --- 3 3 --- 2 4 --- none 5 --- 1 frame lost

These are somewhat approximated since your y subpixel is actually on a value of 0-255, so you gain fractions of pixels for every jump. These are still a good guideline, though.

I also made videos of Ryu climbing up the left wall in 1-1 at these rates to see what the slashes look like. I think my slashes are almost all within the 3-4 frame range, with a few 2's thrown in, and very rarely a 1 or 5. This means that every ~20-30 wallslashes gains me one second.

¤: I think when I tested this it was 2 frames gained, but this is misleading since doing right+a then followed by left+b on the same frame puts you in a strange state where you're facing right as you land on the wall. Doing this consecutively gains more time on average than 1 off and 2 off frame jumps for this reason.