my $graph = new GD::Graph::histogram(600,600);

$graph->set( 
	x_label         => 'Date and Time',
	y_label         => 'Messages',
	title           => 'Number of messages per bin',
	x_labels_vertical => 1,
	bar_spacing     => 0,
	shadow_depth    => 0,
	transparent     => 0,
	histogram_bins     => 10,
	show_values     => 1,
	x_number_format => \&x_format,
	x_tick_number => 10,
);

sub x_format {
	my $value = shift;
	# print $value . " " . localtime(int($value)) . " " . strftime( "%Y-%m-%d %H:%M:%S", localtime(int($value))) . "\n"; # test
	return strftime( "%Y-%m-%d %H:%M:%S", localtime(int($value)));
}

my $timevalues_ref = \@timevalues_secs;
my $IMG;
open($IMG, '> test_plot.png');
binmode $IMG;
print $IMG $graph->plot($timevalues_ref)->png;

close ($IMG);