Most of my plugins rely heavily on WP-Cron, …
Most of my plugins rely heavily on WP-Cron, and this nicely summarizes its behavior. “The WP-Cron functions are not actually cron functions. Instead of executing tasks precisely as scheduled, [WordPress] waits until the front end or admin is loaded, checks if any jobs are scheduled and then fires as needed.” https://wordpress.stackexchange.com/questions/16901/what-causes-wp-schedule-single-event-to-fire-off
What causes wp_schedule_single_event to fire off?