<p>The problem here is that the feed exemple you give doesn't include <a href="http://www.rssboard.org/rss-profile#element-channel-item-pubdate" rel="nofollow">pubDate</a> as a sub-element of each item... wich normaly helps RSS readers to detect new items. And the feed have <a href="https://validator.w3.org/feed/check.cgi?url=http%3A%2F%2Fexport.arxiv.org%2Frss%2Fastro-ph.IM" rel="nofollow">a date fault</a>.</p>

<p>If you were (you are perhaps) in an autopublishing process (i.e. RSS to WordPress) you could employ a <a href="http://www.thesitewizard.com/general/set-cron-job.shtml" rel="nofollow">Cron Job</a> from your web server where you could say... "verify if there's a new item and if yes get it". </p>

<p>My coding skills are not sufficient, sorry, to explain how (on a site I manage, a plugin does this task).</p>
How to keep up with daily changing RSS feed?
<p>I have a webpage that connects to an external site and tries to save some of the information in its RSS feed into MySQL, every time I visit this webpage. The problem is that this site updates its RSS feed daily and so if one day I forget to visit my webpage, the information from the RSS from the external site is lost. Is there a way to retrieve or find the RSS from yesterday if a website daily updates its RSS feed?</p>