The '30 minutes or less' part might be related to the time frame within which the main action or sequence of events in the true story occurs. This can be used to create a sense of urgency or quick - paced action. It also gives the audience an idea of how quickly things unfold in the story.
It might suggest that the story has been condensed or focused on a particular short period of time, which is 30 minutes or less. This could be to highlight a specific moment or series of events that are particularly interesting or important. By basing it on a true story, it adds an element of authenticity. It could also be a marketing gimmick to attract viewers or readers who are interested in short, impactful stories that are based on real - life events.
Well, it could mean that the events in the story, whatever it is, take place within 30 minutes or less in real - time. It might be a way to emphasize the brevity and perhaps the intensity of the story.