Minimum duration: 0.5000s, 00:15:37.9342666 => 00:15:38.4004000
display time = 0.4661s
An event or events within a Timed Text asset have a duration less than 0.5 seconds. The error message provides the timecodes of the affected events and their current durations.
Most, if not all, timed text software allows the user to set a minimum duration threshold and can flag those events that fail to meet it. Retime the highlighted events and redeliver.