WP_Query orderby multiple parameters not working - wordpress

Question

I am trying to sort by my WP_Query results by two meta fields, first date and then time. So effectively
Date A 17:00
Date B 18:00
Date C 07:00
Date B 10:00
Date A 9:00
would be come
Date A 9:00
Date A 17:00
Date B 10:00
Date B 18:00
Date C 07:00
This is my current code:
"post_type" => "event",
"post_status" => "publish",
"posts_per_page" => 25,
"ignore_sticky_posts" => 0,
"show_sticky" => true,
"meta_query" => array(
array(
"key" => "_meta_event_start_date",
"compare" => ">=",
"value" => 0
),
array(
"key" => "_meta_event_start_time",
"compare" => ">=",
"value" => 0
),
),
"order" => "ASC",
"orderby" => "_meta_event_start_date _meta_event_start_time"
It is currently sorting my results appropriately by the date, but not the time (time format is stored hh:mm (24hr)). How might I amend the query to make this work?
I have seen other responses recommending using foreach loops, sql queries or even filters. I can't use these unfortunately as the site I'm working on uses the search plugin Facet WP, and as search requires WP_Query to query the database and output content.
Thanks in advance.

Answer 1

As I see you are trying to order by meta keys - you have to use in this case a quite more complicated syntax according to changes in WordPress 4.2 - something like below:
"post_type" => "event",
"post_status" => "publish",
"posts_per_page" => 25,
"ignore_sticky_posts" => 0,
"show_sticky" => true,
"meta_query" => array(
"event_start_date" => array(
"key" => "_meta_event_start_date",
"compare" => ">=",
"value" => 0
),
"event_start_time" => array(
"key" => "_meta_event_start_time",
"compare" => ">=",
"value" => 0
)
),
"orderby" => array(
"event_start_date" => "ASC",
"event_start_time" => "ASC"
)
Additionally - for single meta_key ordering it is worth to remember that you have to use in the orderby clause values meta_value and meta_value_num