Cria um shortcode para calcular o tempo de leitura na página do post

reading-time.php

<?php
add_shortcode('reading-time', 'reading_time');
function reading_time() {		
	$content = get_post_field( 'post_content', $post->ID );
	$word_count = str_word_count( strip_tags( $content ) );
	$readingtime = ceil($word_count / 200);

	if ($readingtime == 1) {
		$timer = " minuto";
	} else {
		$timer = " minutos";
	}

	$totalreadingtime = $readingtime . $timer;

	ob_start();

	?>
	<span class="reading-time">Tempo de leitura: <?= $totalreadingtime; ?></span>
	<?php

	return ob_get_clean();
}