use strict;
use warnings;

my @times1 = qw( 11:00 13:00 );
my @times2 = qw( 23:00 1:00 );
my @times3 = qw( 10:30 13:00 );
my @times4 = qw( 19:40 1:20 );

print "times1 average: " . average_start_time(@times1) . "\n";
print "times2 average: " . average_start_time(@times2) . "\n";
print "times3 average: " . average_start_time(@times3) . "\n";
print "times4 average: " . average_start_time(@times4) . "\n";

sub average_start_time
{
	my ($hours1, $minutes1) = split /:/, $_[0];
	my ($hours2, $minutes2) = split /:/, $_[1];
	
	my $decimal_hours1 = $hours1 + $minutes1/60;
	my $decimal_hours2 = $hours2 + $minutes2/60;
	
	my $average_decimal_hours = ($decimal_hours1+$decimal_hours2)/2;
	$average_decimal_hours -= 12 if ($decimal_hours1 > $decimal_hours2);
	$average_decimal_hours += 24 if ($average_decimal_hours < 0);
	
	return int($average_decimal_hours) . ":" . sprintf("%02d", ($average_decimal_hours - int($average_decimal_hours))*60);
}