[Metric] Expansion time [Description] 
For Rich Media Expanding creatives, the amount of time, in seconds, that an expanded creative was displayed in its expanded state. Any expansion times that exceed several minutes are capped. Extended expansion time can occur, for example, when a user opens an expanding ad then steps away for an hour without collapsing the ad or closing the browser. The capping rule helps prevent skewed results for average display time in reporting. While this event is counted only once per impression (see Rich Media expansions, below), the time that the ad remains in an expanded state is recorded as the total expansion time. For example, if a user expands an Expanding ad for 10 seconds, and then the same user expands the ad a second time for 10 seconds, the number of expansions is recorded as one, and the total expansion time is recorded as 20 seconds.