The Bus did not arrive at the time stated by the App/Website
The real time system is by its nature dynamic and is set to respond to factors on the road, including changes in traffic patterns, accidents, etc. In general though, the margin of error is less than one minute for predictions of five minutes away or less. For ten-minute predictions, the margin of error is less than two minutes, the margin increases the further away in time the prediction is, as the probability of intervening events increases. The system is continually fine-tuned in response to testing and feedback.