Add Yoast reading time post meta before posts content

jba-yoast-reading-time.php

<?php
/**
 * Plugin Name: Add Yoast reading time post meta before posts content.
 * Author: Jb Audras
 * Version: 0.1
 * Author URI: https://whodunit.fr
 */

/**
 * Gets Yoast reading time and add it before the content.
 */
function jba_yoast_reading_time( $content ) {
	global $post;
	if ( is_plugin_active( 'wordpress-seo/wp-seo.php' ) || is_plugin_active( 'wordpress-seo-premium/wp-seo-premium.php' ) ) {
		$yoast_estimated_time = YoastSEO()->meta->for_post( $post->ID )->estimated_reading_time_minutes;
		// Because we don't want to show 0 minutes…
		$yoast_estimated_time = $yoast_estimated_time > 0 ? $yoast_estimated_time : 1;

		$content = '<p>Est. reading time : ' . $yoast_estimated_time . ' minutes.</p>' . $content;
	}
	return $content;
}
add_filter( 'the_content', 'jba_yoast_reading_time' );