WordPress Countdown Timer Shortcode

functions.php

<?php 
/*
 *
 * Countdown Timer Shortcode
 * [cdt month="9" day="28" year="2021"] This is content that will only be shown after a set number of days.[/cdt]
 *
 */
// @codingStandardsIgnoreStart
function aet_content_countdown($atts, $content = null){
  extract(shortcode_atts(array(
     'month' => '',
     'day'   => '',
     'year'  => ''
    ), $atts));
    $remain = ceil((mktime( 0,0,0,(int)$month,(int)$day,(int)$year) - time())/86400);
    if( $remain > 1 ){
        return $daysremain = "<div class=\"sitelunch\"><h4>Countdown to launch!</h4><span class=\"sitelunchdays\">$remain</span><h4>days</h4></div>";
    }else if($remain == 1 ){
    return $daysremain = "<div class=\"sitelunch\"><h4>Countdown to launch!</h4><span class=\"sitelunchdays\">$remain</span><h4>day</h4></div>";
    }else{
        return $content;
    }
}
add_shortcode('cdt', 'aet_content_countdown');
// @codingStandardsIgnoreEnd