I know a larger part of this question is "it depends", since scales matter here. Let's bound ourselves to desktop 3D-printed objects, which will typically be no more than a few cm thick.
After an hour or so of acetone vapor smoothing, some people have noticed that ABS parts can bubble a week or two later. Below is an example of where an ABS part deformed when exposed to constant heat.
It makes sense to me that once the acetone is subsurface that it will just as easily continue to work its way deeper into the part as head toward the surface and evaporate.
On a long enough time line, though, all the acetone will eventually work its way to the surface and liberate itself from the plastic.
How can I determine that timeline? I would have thought it was hours, but empirical evidence seems to suggest it's at least weeks, if not longer.
(I'm making an assumption here and that's that acetone is a harmless solvent and will not permanently modify the plastic. It's unclear if that assumption is completely correct.)