Using DateTime, that I prefer to Date::Calc, finding it much more clear to code :

use DateTime;

$dt1 = DateTime->new(year   => 2004,
                     hour   => 16,
                     minute => 54,
                     second => 23);

$dt2 = DateTime->new(year   => 2004,
                     hour   => 16,
                     minute => 54,
                     second => 28);

# Beware : $diff is a DateTime::Duration object 
# (which is logical if one think about it...)
$diff = $dt2 - $dt1;
print $diff->hours, ":", $diff->minutes, ":", $diff->seconds, "\n";
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HTH