swissknife, Here's a high level design for your code regards to dates/times.. By using the "Date::Manip" module you can parse many date formats and calculations..

#!/usr/bin/perl

use Date::Manip;



$val = "<MessageDateTime v=\"2014-03-18T15:41:14Z\" \/\>";

($ftime) = ($val =~ /\=\"(.*)\"/);
print "FTIME: \"$ftime\"\n";

$ftime =~ s/\T/ /;
print "FTIME: \"$ftime\"\n";

$parse = &ParseDate($ftime);
print "PARSE: \"$parse\"\n";

$eptime = UnixDate($parse, "%s");
print "EPTIME: \"$eptime\"\n";

$ct = 0; $ct = 15; $septime = undef; $time = undef;
$septime =  UnixDate(ParseDate("$ct minutes ago"), "%s");
print "$ct MINUTES AGO: \"$septime\"\n";


if($eptime > $septime)
  {
  print "EPTIME: \"$eptime\" IS MORE THEN SEPTIME \"$septime\".. KEEP 
+FILE\n";
  }
 else
  {
  print "EPTIME: \"$eptime\" IS -NOT- MORE THEN SEPTIME \"$septime\"..
+ NEXT\n";
  }


OUTPUT:

FTIME: "2014-03-18T15:41:14Z"
FTIME: "2014-03-18 15:41:14Z"
PARSE: "2014031811:41:14"
EPTIME: "1395157274"
15 MINUTES AGO: "1395163449"
EPTIME: "1395157274" IS -NOT- MORE THEN SEPTIME "1395163449".. NEXT
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If the time in the file is more then 15 minutes ago keep the file else next. NOTE: I prefer nowadays to use date::manip due to flexibility.