Wordpress ordered by two custom fields meta_key's - php

Question

I have a Woocomerce query working with one meta_key ( 'countdown_date' or 'hour' ).
It sorts the products by a custom 'meta_key' => 'countdown_date' or 'hour' and orders them using 'orderby' => 'meta_value_num'.
I need to join two meta_key's together. ('hour' key only returns the first two ints of a 24hr time).
Result required, products ordered by two custom fields countdown_date and hour
$args = array(
'posts_per_page' => 20,
'tax_query' => array(
'relation' => 'AND',
array(
'taxonomy' => 'product_cat',
'field' => 'slug',
'terms' => 'live-events'
)),
'post_type' => 'product',
'meta_key' => 'countdown_date',
// need to add second meta key here 'meta_key' => 'hour',
'orderby' => 'meta_value_num',
'order' => 'ASC'
);
$the_query = new WP_Query( $args );
I've looked at loads of similar questions with no results.
Two loops seems overkill and adding the meta_query is not working for me.
Any help would be great. :)
Full working code in the answer below from #Rene_Korss
Could i get a hand add this to functions.php so that the archive will sort the same way as the custom loop.
Below is a simplified version of the function i've got working. I need to add the two meta_key's here too.
add_filter('woocommerce_get_catalog_ordering_args','wdm_change_ordering',10,1);
function wdm_change_ordering($args) {
if(is_product_category()) {
$args['meta_key'] = 'countdown_date';
// need to add second meta key here $args['meta_key'] = 'hour',
$args['orderby'] = 'meta_value';
$args['order'] = 'ASC';
}
return $args;
}

Answer 1

Add both meta keys to meta_query and set orderby to meta_value. Then you can replace it with posts_orderby hook.
<?php
// Override orderby if orderby value = 'meta_value'
function orderby_countdown_date_and_hour( $orderby ){
return str_replace( 'meta_value', 'meta_value, mt1.meta_value', $orderby );
}
$args = array(
'post_type' => 'product',
'posts_per_page' => 20,
'tax_query' => array(
'relation' => 'AND',
array(
'taxonomy' => 'product_cat',
'field' => 'slug',
'terms' => 'live-events'
)
),
'meta_query' => array(
array(
'key' => 'countdown_date',
'value' => '',
'compare' => '!='
),
array(
'key' => 'hour',
'value' => '',
'compare' => '!='
)
),
'orderby' => 'meta_value',
'order' => 'ASC'
);
// Replace orderby
add_filter( 'posts_orderby', 'orderby_countdown_date_and_hour' );
// Query
$the_query = new WP_Query( $args );
// Remove our orderby
remove_filter( 'posts_orderby', 'orderby_countdown_date_and_hour' );
This results in
ORDER BY dbprefix_postmeta.meta_value, mt1.meta_value ASC
which means
ORDER BY countdown_date, hour ASC