The window to perform a jump off a ladder/chain/vine: (assuming you were at the left or right edge of the vine)

Holding left or right only: All characters (afaik): 1 frame Holding left or right, and up: Mario/Toad/Princess (afaik): 3 frames -with Luigi: 8 frames (easy to mash)

Holding A can increase the window to jump with Luigi. The gap between holding and pressing A shortens each frame, down to an only 1 frame gap (on the 12th frame following the first frame available to jump), so you probably could only feasibly add up to 4 more frames to the total jump window.