When it comes to how long an alert is displayed, the display time variable is a secondary priority to the length of the attached sound file for an alert. The alert will be active for at least as long as the audio clip attached to it is playing. So if for instance you have a 20 second audio file on an alert with a 5 second display time, the display time would be ignored since the audio isn't finished playing. If you had a 3 second sound file and a display time of 5 seconds, the alert would display for the full duration set by the display time.
keywords: display time, audio, sound, alerts