A summary event log filter allows for events to be collected over a period of time rather than sending you an alert or performing an action immediately. You can turn any Event Log filter to a summary event filter by clicking the "Hour/Day" tab and setting the schedule type to "Summary."
If an event occurs during the specified time period, then the event will be collected and sent out at the end of the time period.
This is best explained with the example above: Events occurring between 08:00 and 17:00 will be cached and sent out at 17:00 - the end of the time period. Events that take place outside the configured time period will not be processed by this filter (and ignored).