I use the following code to run a task. this doesn’t require adding a cron schedule.
function setup_my_action() {
if (!wp_next_scheduled('my_action')) {
wp_schedule_single_event(time()+3600, 'my_action');
}
}
function my_action() {
// do something
}
add_action('init','setup_my_action');
add_action('my_action', 'my_action');