Scheduled Rules vs. Run Time Rules
Each Alert Rule dictates the schedule for a policy and they are either time-based or dynamic.
Some rules are time-based, because they examine a group of events and have a pre-defined schedule (you can modify the schedule). The data collected requires a time period to extract meaningful values. For example, to derive a percentage of failures, you must collect more than one backup job. It is the time period in between runs that is examined for the conditions you set in the Alert Policy.
Some rules are dynamic - every time data is collected that matches the criteria set in the Alert Policy, the alert is triggered. These real-time Alert Rules deliver instant results using the notification method defined in the policy.