Scheduling a Wordpress Cron Job (with custom schedule)

functions.php

<?php
//This is how to set up a cron job via PHP in WordPress. 
//Do not rely on simply adding it via a plugin like WP Crontrol, as WordPress occasionally loses cron jobs or fails to reschedule them.

//1. Add the function you want to run regularly, and an action which will trigger the function.
function mytheme_cron_function(){
  //Do some things... your custom code goes here.
}
add_action('mytheme_cron_hook','mytheme_cron_function');//name of action, name of function to run

//2. Add 10-min cron schedule. This is just an aribtrary interval of seconds, with a name.
function mytheme_add_ten_minute_schedule( $schedules ) {
  
    if(!empty($schedules['ten_minutes'])) return $schedules; //don't overwrite if this schedule already exists
  
    $schedules['ten_minutes'] = array(
        'interval' => 600, //seconds
        'display' => 'Every 10 mins'
    );
    return $schedules;
}
add_filter( 'cron_schedules', 'mytheme_add_ten_minute_schedule' );

//3. Add cron job if not already scheduled
$args = array();
if ( ! wp_next_scheduled( 'mytheme_cron_hook', $args ) ) {
    wp_schedule_event( time(), 'ten_minutes', 'mytheme_cron_hook', $args );
}