Orders in our system are usually sent immediately. However, if for some reason an order cannot be sent right away, it is placed in a queue to be sent after 1 minute. This queue is processed either on a schedule (cron), or when a user visits the site.
If the queue is set to be processed by cron, but cron is not running, then orders will not be sent. Similarly, if the queue is set to be processed when users visit the site, but users do not visit the site, orders will also not be sent.
Recommendation: For more reliable and timely order dispatch, it is recommended to move everything to cron processing and make sure that cron is active. You can read more about how to set up and activate cron in WordPress in this article.