2.5 years later, I have the same question.
Anyone have any insights and/or sources they can point to for a definitive answer? With regards to travel, I wonder whether and/or how far a successful possession using the malevolence ability would enable a ghost to travel from its anchor point (which may or may not be the place where its physical remains might be found)?
Is there a time limit on possession? Is it the same as the magic jar spell?
Thanks in advance for your feedback.
My guess is that this has been kept vague to give GMs something to work with.