Relevanssi search date through content and through published date

functions.php

// Inspired by : https://www.relevanssi.com/knowledge-base/natural-language-date-queries/?replytocom=264649#respond 

add_filter('relevanssi_modify_wp_query', 'rlv_date_query');
function rlv_date_query($query)
{
    if (substr($query->query_vars['s'], 0, 10) === "published:") {
        // Remove "published:" from search string.
        $query->query_vars['s'] = substr($query->query_vars['s'], 10);

        // If The query string is a year... (We check that it's an integer between 1900 and current year)
        if ((int) $query->query_vars['s'] > 1900 && (int) $query->query_vars['s'] <= date("Y")) {

            $date_query = [
                'column' => 'post_date',
                'year'   => $query->query_vars['s'],
            ];
            $query->set('date_query', $date_query);

            // Empty search. (@TODO removed consumed part of the search string so we can search for something at a date.)
            $query->query_vars['s'] = '';

        }

        // If the actual search string convert to a timestamp!
        // Support almost any "Natural language" date with or without year.
        else if ($time = strtotime($query->query_vars['s'])) {
            $year       = date('Y', $time);
            $use_year   = strpos($query->query_vars['s'], $year) !== false;
            $month      = date('m', $time);
            $day        = date('d', $time);
            $date_query = [
                'column' => 'post_date',
                'month' => $month,
                'day'   => $day,
            ];
            
            if ($use_year) {
                $date_query['year'] = $year;
            }
            $query->set('date_query', $date_query);

            // Empty search. (@TODO removed consumed part of the search string so we can search for something at a date.)
            $query->query_vars['s'] = '';
        }
    }

    return $query;
}

search.php

<!-- Heading of the page -->
<?php 
  if (substr($_GET['s'], 0, 10) === "published:") {
      echo '<span>' . __("Search articles and books published on:") . substr($_GET['s'], 10) . '</span>';
  } else {
      echo '<span>' . __("Search results for:") . $_GET['s'] . '</span>';
  } 
?>

<!-- Under the search form -->
<?php 
  if (strtotime($_GET['s'])) {
      echo __("Not the result you where expecting? We’ve detected that you might have entered a date. Would you like to ") . ' ' . '<a href="' . get_site_url() . '/?s=published:' . $_GET['s'] . '">' . __('search by publication date') . '</a> '.__('instead of content ?');
  } else {
      echo __("Not happy with the results? Please try another search.");
  } 
?>