Hmm, here's how I'd add times (stretched out a bit to make it easier to read) - probably not the most efficient but... TIMTOWTDI :)

my $time1 = '4:23';
my $time2 = '5:13';

my $total_time = add_times($time1,$time2);
print "Total time: $total_time\n";
exit(0);

sub add_times {

  # read in times sent
  my @times = @_;

  my ($hours,$mins);

  for (@times) {

    # get values for this time
    my ($this_hour,$this_min) = split /:/;

    # keep running total
    $hours += $this_hour;
    $mins  += $this_min;
  }

  # no of hours stored in $mins
  $hours += int($mins/60);

  # remainder after deviding by 60
  $mins  %= 60;

  return "$hours:$mins";
}
[download]

With this sub being able to take as many times as you want to send to it...

cLive ;-)