XML::Simple will read in and write out your XML file. If you want to change the data, you need to search through the data hash it provides and make the changes yourself. OTOH, this is a trivial XSL transformation for something like XML::XSLT:

#
#  Here's the stylesheet.  The annoying part is that the
#  actual change is three lines, the rest is grammar.  You
#  can add multiple templates to make simultaneous changes.
#
my $xsl = <<EOS;
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" versi
+on="1.0">
 <xsl:output method="xml" indent="yes"/> 

 <xsl:template match="/">
    <transform>
       <xsl:apply-templates/>
    </transform>
 </xsl:template>

 <xsl:template match="//time">
   $new_time
 </xsl:template> 

</xsl:stylesheet>
EOS

#
# The perl is down here
#
use XML::XSLT;

my $xslt = XML::XSLT->new ($xsl, warnings => 1);
$xslt->transform ($xmlfile);
print $xslt->toString;
$xslt->dispose();
[download]

This same tool could also answer your question in how to replace the <anon> tag (XML::Simple).