How can I find out for how long a particular video has been watched?

You can analyze the stats for a single video by going into your Video Stats Center (located in your Lightcast.com Control Center) and select a video of your choice by using the drop down filter "ALL Videos". You can also choose a specific day with the calendar feature on top and a specific continent, country, region or city. By using these filters you will receive stats for a specific video, watched on a selected day in a selected area.