WooCommerce Cross Seller works by monitoring when an order is marked as Complete and then scheduling individual CRON events.
Each CRON event triggers an email and by using the timing feature for one-off CRON events we do not need to keep a separate database table to keep these events.
Each event is only triggered when the scheduled time is reached or after if your website did not trigger a CRON event at the right time.
Note - you can change the desired order status in the settings page if you have a custom setup.
Resetting an order
If you change the status of an order previously marked Complete any scheduled email to that customer will be unscheduled.
if and when you set the status back to Complete the emails will be rescheduled but starting from the moment you set the order to complete again.