Q: How is usage time measured or captured?
Amazon captures app usage based on Resume, Pause and Stop events in the Android app lifecycle. Apps that close prematurely and do not trigger these events will have reduced accuracy in usage measurement. Amazon recommends that developers manage app crashes and activity lifecycle events appropriately to ensure accurate usage measurement.
One more reason to close app using activity lifecycle. Or kill it inside onDestroy method, like @vkrishna advicied.