Example of how to add some additional text after the datetime filter checkbox section/before the ticket selector

using_js_method.php

<?php //Please do not include the opening PHP tag if you do not already have one

//This adds text after the datetime selector using Javascript.
function tw_ee_add_message_after_datetime_checkboxes() {
    if( is_single() ) {
        wp_add_inline_script( 
        'ticket_selector',
        'jQuery(document).ready(function ($) {
            var $checkbox_dropdown = $(".checkbox-dropdown-selector-wrap-dv");
            $checkbox_dropdown.after(
                "<span class=\'important-notice\'>Some additional text</span>"
            );
        });'
        );
    }
}
add_action( 'wp_enqueue_scripts', 'tw_ee_add_message_after_datetime_checkboxes', 11 );

using_php_method.php

<?php //Please do not include the opening PHP tag if you do not already have one

function tw_ee_add_text_before_ticket_selector() {
    echo "<span class='important-notice'>Some additional text</span>";
}
add_action('AHEE__ticket_selector_chart__template__before_ticket_selector', 'tw_ee_add_text_before_ticket_selector');