EnGage will automatically generate a program loop duration within each zone.  As content is added or removed, it will instantly adjust.

Note that the zone's total duration in the Program Designer is not an accurate representation when using any dynamic content widget or OSM widget. This is because it includes the duration of the widget itself. It does not show the duration of dynamic content or OSM content that the widget is going to select/play. This can be estimated by finding the average duration of all assets tagged/scheduled to play. Subtract the widget's duration from the zone total then add the average duration of all tagged/scheduled assets.