Why does the Activity Tab have a shorter time frame than what was specified during report generation?
The Activity tab will have the time frame of when the SQL ID was sampled. If it was not active during the entire time specified during report generation, the Activity tab will show a shorter timeline. In this example, the report was generated from 3:41:35 to 4:41:35 (as seen in the top right of the screen), but the timeline in Activity only shows ~8-10 minutes when the SQL statement was sampled in ASH.