The Expiration date is calculated automatically and cannot be changed manually. If the dynamic segment is not used in the reports, then the segment will be deleted when you reach the Expiration date. Otherwise, the Expiration date is prolonged. Also, if you change the settings for the dynamic segment, all the previously collected data resets and we start collecting data in accordance with the new settings. Static segments have the Expiration date as well, but still, segments of this type are not being cleared or terminated.