Hello,
First of all, thank you for your purchase.
You can improve the scheduling accuracy of the plugin if you replace the wp_cron module of WordPress with a server side cron.
wp_cron is a default system WordPress uses to schedule tasks automatically, but it has a major flaw: it requires website visitors to access your page for it to function. Because of this, I recommend replacing it with server side cron. Please check details on how to do this, here: https://themeisle.com/blog/disable-wp-cron/
Regarding individual scheduling of rules, I noted your idea, but this is not possible at the moment. The only way is to create rules which don’t run at the same time (have different scheduling times). If you combine this with the server side cron replacement, it will run in a more precise way.
Let me know if this helped.
Regards, Szabi – CodeRevolution.