date_test.pl

#!/usr/bin/perl
use strict;
use warnings;
use DateTime;
use POSIX::strptime;

my $date1a = parse_date('03-SEP-10');
my $date1b = parse_date('01-JAN-13');
my $days1d  = $date1a->delta_days($date1b)->days;
my $days1dd = $date1a->delta_days($date1b)->delta_days;
print "$days1dd != $days1d\n"; #prints 851 != 4

my $date2a = parse_date('16-OCT-01');
my $date2b = parse_date('01-JAN-13');
my $days2d  = $date2a->delta_days($date2b)->days;
my $days2dd = $date2a->delta_days($date2b)->delta_days;
print "$days2dd != $days2d\n"; # prints 4095 != 0

sub parse_date {
    my ($mday, $mon, $year) = (POSIX::strptime($_[0], '%d-%b-%y'))[3,4,5];
    return DateTime->new(
        year  => $year,
        month => $mon + 1,
        day   => $mday,
    );
}