How do I control the duration for each image in my MRSS feed?

You can control the length of time each image plays by editing the media RSS feed file (i.e. the file that is remotely hosted and the player periodically retrieves).  Below is an item element from an MRSS feed file. In the "<media>" tag, the duration is set to 10 sections for that image. 

<item>
<title>image1</title>
<link>https://brightsignnetwork.com/download/MRSS/image1.jpg</link>
<category>image</category>
<description>image1 is the best</description>
<guid isPermaLink="false">0624</guid>
<media:content url="https://brightsignnetwork.com/download/MRSS/image1.jpg" fileSize="255817" type="image/jpeg" duration="10"/>
</item>

Note: The "fileSize" (in bytes) of each media file must be included to avoid multiple downloads of the same file even when it hasn't changed.