conditional OR 1

$meta_query = array(
	'relation' => 'AND',
	array(
		'key'     => 'exibitions_$_date',
		'value'   => 'current_time('Ymd')',
		'compare' => '=',
	),
	array(
		'key'     => 'exibitions_$_time',
		'value'   => 'current_time('H:i:s')',
		'compare' => '>',
	),
);