I know, vaguely, how the story will end. I do know a great deal of how starts. But the big question is how much stuff goes in the middle when the characters are regrouping and putting together a plan to attack. They do not want to put it off too long, the villainesses are up to vileness, but by the same token, they don't want to risk failure.
Much, I think, turns on how quickly they can discover what they need to know to undo something vile one villainess did in the beginning. Especially because it is magical. But I still have to world-build their ways to find out.
Which will, of course, determine whether it's a novel or a short story, even if I have to build up the beginning and ending to meet the structure.
(Multi-point-of-view points toward longer.)