NNTP spec supports this command for you get a list of article numbers received after a given time point:

NEWNEWS newsgroups date time [GMT] [<distribution>]
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In your Perl script, just do something like:

require News::NNTPClient;
 
  $c = new News::NNTPClient;
 
  foreach ($c->newnews("test", time - 3600)) {
      print $c->body($_);
  }
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You either run your script as a daemon, or use whatever scheduler you have to schedule it to run periodically.

Update:

If the news group you are trying to access falls in liz's description, then you have to remember the number of the last article, and next time, just start from there. Remember one thing, article number are not neccessary continuous, and your script has to expet this.