conditional time check

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