For how long do monsters possess someone?

Question

When for example a Fey or a ghost possesses someone, it says that it works similar to the "magic jar" spell. Does that mean that they can only possess someone for the duration of the spell (hours per level) or is it more?

Answer 1

Unless the creature's magic jar effect says otherwise, a creature's magic jar effect is just like the spell magic jar, inheriting both the spell's strengths and weaknesses—like its limited duration (1 hour/level) and the fact that a target that makes a successful saving throw against the magic jar effect "automatically succeeds on further saving throws if you [i.e. the monster] attempt to possess its body again."

Specific creatures may have exceptions that change how their magic jar effect works when compared to the spell (one of the most common being the vague and unruly without a receptacle). A magic jar effect with a longer than normal duration—or even a permanent duration—should mention that extended duration in the description of the creature's ability.