Timespan Tool
Timespan tags restrict the visibility of data to a specific period of time. Timespans are usually used for data sets that appear in multiple locations (e.g., Placemarks moving along a path). The data associated with a timespan is visible only when the time slider is showing the time interval defined in the timespan tag.
The timespan for an individual object can be set in its property sheet. Similarly, the timespan for a group can be set from the group property sheet, when you want all objects in the group and all subgroup objects to have the same timespan. The Timespan Tool is necessary when you want to evenly split a timespan, either between a group’s subgroups or between all the objects in all of a group’s subgroups.