<?php // in functions.php
/**
 * Adds custom merge tags in Gravity Forms.
 *
 * @since 10/2019
 * @author Alexander Persky
 */
function add_merge_tags($form) { ?>
    <script>
        function add_merge_tags(mergeTags, elementId, hideAllFields, excludeFieldTypes, isPrepop, option) {
            mergeTags['custom'].tags.push(
                {
                    tag: '{current_day}',
                    label: 'Current Day'
                },
                {
                    tag: '{current_time}',
                    label: 'Current Time'
                }
            );

            return mergeTags;
        }
        gform.addFilter('gform_merge_tags', 'add_merge_tags');
    </script>
<?php
    return $form;
}
add_action( 'gform_admin_pre_render', 'add_merge_tags' );


/**
 * Adds custom merge tag in Gravity Forms.
 *
 * This tag displays the day of the week.
 * Eg: Monday
 *
 * @since 10/2019
 * @author Alexander Persky
 */
function gf_add_current_day($text, $form, $entry, $url_encode, $esc_html, $nl2br, $format) {
    $custom_merge_tag = '{current_day}';

    if (strpos($text, $custom_merge_tag) === false) {
        return $text;
    }

    $current_day = date('l');

    $text = str_replace($custom_merge_tag, $current_day, $text);

    return $text;
}
add_filter('gform_replace_merge_tags', 'gf_add_current_day', 10, 7);

/**
 * Adds custom merge tag in Gravity Forms.
 *
 * This tag displays the hour of the day in 24hour format with leading zeros.
 * Eg: 00-24
 *
 * @since 10/2019
 * @author Alexander Persky
 */
function gf_add_current_time($text, $form, $entry, $url_encode, $esc_html, $nl2br, $format) {
    $custom_merge_tag = '{current_time}';

    if (strpos($text, $custom_merge_tag) === false) {
        return $text;
    }

    $current_day = date('H');

    $text = str_replace($custom_merge_tag, $current_day, $text);

    return $text;
}
add_filter('gform_replace_merge_tags', 'gf_add_current_time', 10, 7);