add_action( 'wp_async_save_post', 'josh_send_to_api' );
function josh_send_to_api( $id ) {
    wp_mail( 'abc@test.com', date("H:i:s", time() ), $id );

    sleep(25);
    wp_mail( 'abc@test.com', date("H:i:s", time() ), $id );
}

class Josh_Task extends WP_Async_Task {
    /**
    * Action to use to trigger this task
    *
    * @var string
    */
    protected $action = 'save_post';

    /**
    * Prepare POST data to send to session that processes the task
    *
    * @param array $data Params from hook
    *
    * @return array
    */
    protected function prepare_data($data){
        return array(
            'post_id' => 5
        );
    }

    /**
    * Run the asynchronous task
    *
    * Calls send_to_api()
    */
    protected function run_action() {
        if( isset( $_POST[ 'post_id' ] ) && 0 < absint( $_POST[ 'post_id' ] ) ) {
        do_action( "wp_async_$this->action", 5 );
        }
    }
}

new Josh_Task();