This is the duration of the advert track. This is expressed in whole seconds and is used by the advert schedule to ensure an advert block does not over duration. This field is automatically populated when you choose a track or audio file. This duration is usually best kept at a multiple of 5 (e.g. 5, 10, 15, 30 seconds) in order to help the scheduler fit adverts into whole minutes, such as 1 minute, 2 minutes.