title: What is expected DATETIME format for Wordpress Codex WP Meta Query parameter?
body: <p>This docs:</p>
  
  <p><a href="https://codex.wordpress.org/Class_Reference/WP_Meta_Query" rel="nofollow noreferrer">https://codex.wordpress.org/Class_Reference/WP_Meta_Query</a></p>
  
  <p>Tells you can compare DATETIME values. </p>
  
  <p>What is expected format of DATETIME for WP_Meta_Query?</p>