The nas storm mechanism is actually driven by the entry of new alarms into the period window.
When a new alarm arrives, the nas looks at the list of alarms starting from NOW and going back in time for the period set (e.g. 5 mins.). Any alarms older than the current now - 5 mins are deleted from the list and removed from quarantine. Then the list is counted. If the window contains a number of alarms exceeding the threshold, a storm exists and the incoming alarms receive the NAS_QUARANTINE subject. If the remaining alarms fall below the threshold in number then the storm condition ceases to exist.
The entire process is repeated on the arrival of the next alarm. So storm protection is not based on a clock sampling interval.