Logic do add the date to the post of blauwzwartfans.be

bzf.php

function addDateBeforeFirstParagraph($content) {
        if(!is_singular('post')) return $content;
        $closing_p = '<p>';
        $paragraphs = explode( $closing_p, $content );
        foreach ($paragraphs as $index => $paragraph) {

                if ( trim( $paragraph ) ) {
                        $paragraphs[$index] .= $closing_p;
                }

                if ($index == 2) {
                        $paragraphs[$index] = '<span>'.get_the_date('d F Y H:i').' - </span>'.$paragraphs[$index];
                }
        }

        return implode( '', $paragraphs );
}
add_filter( 'the_content', 'addDateBeforeFirstParagraph' );