instances metadata

$meta_query = array(
	'relation' => 'AND',
	array(
		'key'     => 'start_selling_datetime',
		'value'   => 'time()',
		'compare' => '<',
	),
	array(
		'key'     => 'stop_selling_datetime',
		'value'   => 'time()',
		'compare' => '>',
	),
	array(
		'key'     => 'cancelled',
		'value'   => '1',
		'compare' => '!=',
	),
	array(
		'key'     => 'on_sale',
		'value'   => '1',
		'compare' => '=',
	),
);