Blending too much is what causes emusions, how long it takes to separate is a function of how viscous the bark soup is, which in turn is affected by bark to water ratio and how powdered the bark is.
I find a little on the watery side works fine and starts to separate within seconds of stopping mixing, but will take a few minutes to finish the job. You can tell it's finished because interface between the layers becomes flat and smooth, before that it's disturbed by bubbles of NPS coming back out the soup and you get a bit of a frothy boundary.
If it's too thick then there will be a few minutes before any clear layer starts to show, and often the soup seems to hang on to 10ml or more of my NPS when it does that.
Repeating mild mixings, allowing full separation between repeats, is better than shaking it up vigorously in terms of emulsion risk.