You appear to be able to stay hovering as long as you keep sneaking and don't move away from where the vine originally was.

I've found this works on my original survival world, which is converted from an earlier 1.18 snapshot, and a world I've created on 1.18 Pre-release 2 for the reason to test this.

Update: I can confirm that this still exists in 1.18 Pre-release 3, with both vines and ladders