I am not familiar with XML::XPath but I have used XML::Simple, which might be a suitable alternative (if you're restricted to using XPath, just file the rest of this post away for future reference). If your XML input file isn't too big, you could do something like this:

use strict;
use warnings;
use XML::Simple;

# read in the XML data file
open( INFILE, '<', 'xml_input_file.xml' )
    or die "error opening input file!";
undef $/; # slurp mode
my $infile = <INFILE>;
close INFILE;

# parse the XML file using XML::Simple
my $dataref = XMLin( $infile );

# view the parsed data structure
use Data::Dumper;
print Dumper( $dataref );
[download]

I didn't code the rest (where you find a record given a date), but if you understand references it should be straightforward after seeing how the file is parsed (with Data::Dumper). If you decide to go this route and need help pulling out the data, just ask.
HTH