What is the scrpt you have on that? It's very likely
PromptLocal is hard coded and you can't change the duration as it does not have a duration, whether it is shown or not is determined by your script and how it shows the text. What's probably happening here isn't a duration issue, but a distance/angle of sight issue, when you turn to the other one then the first one so close to the second one that it is probably still on the edge of the distance or angle you required in your script
PromptDuration is an entirely separate command, it's the same as the normal Prompt but on a timer, it doesn't effect PromptLocal.
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