Hey USD SmartAlerts,
I'm pretty sure you've already configured it as you shared you have to set to 3 times daily - however the intervals can only be configured on the same pane where you select the day/time within the spam quarantine notifications settings.
So the only means I can say to send more notifications is daily and set more hourly notifications.
One thing to note with notifications is - if there has been no new emails that matched the end user spam quarantine; new notifications will not be sent even if it's set hourly to avoid duplicate notifications.
Regards,
Mathew