The threshold period is the length of time that status messages are counted before starting over at zero. If there were no threshold period, every status message threshold, no matter how high, would eventually be crossed, but it would not be meaningful; a hundred messages in 3 months is not as significant as a hundred messages in one day.
Therefore, choose a threshold period appropriate for how often you plan to check the status summarizer. The threshold period should be the same as or greater than how often you plan to check the status summarizer; that way, any threshold crossings will not get reset before you have a chance to look at them.
Configure the Component Status Summarizer
Status Messages Overview