This setting, “Stack blacklist monitor notifications for X hours”, can be found on your “Account Settings” page:

When we designed the notification system, we wanted to avoid our platform spamming your inbox with notifications, considering that some clients monitor thousands or tens of thousands of IPs. Sending out an email to each one of them would have been unacceptable. So we’ve decided to stack these notifications and send them out every X hours. X is the number in this setting.

It can be as low as 10 minutes, which means that your notifications are only stacked for 10 minutes, then sent out. It can be as high as 24, which means that all of your notifications will be stacked and sent to you just once per day.

If you want to be notified as quickly as possible once changes are detected in any of your blacklist monitors, then select the 10 minutes value.