[WordPress] Define a custom schedule for cron jobs to run within the context of WordPress.

wordpress-weekly-cron-schedule.php

<?php

add_filter( 'cron_schedules', 'acme_add_weekly_cron_schedule' );
/**
 * Adds a weekly interval to the WordPress scheduled tasks.
 *
 * Accepts an array of schedules that WordPress current defines for its
 * scheduled tasks, and introduces a new weekly interval that can be used
 * via the API.
 * 
 * The interval is defined by using a week (in terms of seconds) and will be
 * displayed as 'Once Daily' in the dashboard (when using a cron viewer) such
 * as Cron View (https://wordpress.org/plugins/cron-view/).
 *
 * @param  array $schedules The array of schedules that WordPress provides.
 * @return array The updated schedules with the weekly interval defined.
 */
function acme_add_weekly_cron_schedule( $schedules ) {

    $schedules['weekly'] = array(
        'interval' => 604800,
        'display'  => 'Once Weekly'
    );

    return $schedules;
    
}