Posted date format not reflected

I found a workaround by myself. In wp-content/themes/twentythirteen/function.php:

function twentythirteen_entry_date( $echo = true ) {
:
    //$date = sprintf( '<span class="date"><a href="https://wordpress.stackexchange.com/questions/112514/%1$s" title="%2$s" rel="bookmark"><time class="entry-date" datetime="%3$s">%4$s</time></a></span>',
    $date = sprintf( '<span class="date"><a href="https://wordpress.stackexchange.com/questions/112514/%1$s" title="%2$s" rel="bookmark"><time class="entry-date" datetime="%3$s">%3$s</time></a></span>',

x %4$s

o %3$s

---

Still, it doesn’t seem to reflect the choice of the date-format setting made on wp.