Display the latest posts, published in the last hour, with WP_Query

You can try the following to query for last hour posts:

'date_query' => [
     [
         'after'     => '1 hour ago',  
         'inclusive' => true,
     ],
 ],

or

'date_query' => [
     [
         'after'     => 'last hour',  
         'inclusive' => true,
     ],
 ],

or

'date_query' => [
     [
         'after'     => '-1 hour',  
         'inclusive' => true,
     ],
 ],

Here we are playing with the strtotime() support in date_query.