#!/perl/bin/perl -w

use strict;
use Time::Local;

my $endtime     = "17:39:31";
my $starttime   = "17:07:53";

my @end         = split(":", $endtime);
my @start       = split(":", $starttime);

my $end_epoch   = timelocal(reverse(@end), 1,1,2007);
my $start_epoch = timelocal(reverse(@start), 1,1,2007);

my $elapsed     = $end_epoch - $start_epoch;

my $hours       = int($elapsed / 3600);
my $left        = $elapsed - $hours * 3600;
my $minutes     = int($left / 60);
my $seconds     = $left % 60;

printf "%02d:%02d:%02d\n", $hours, $minutes, $seconds;

__OUTPUT__
00:31:38