[Uptime reporting] Uptime - adjust time before alert emails me

How do I adjust the time required when a site is \"down\" and the email is sent. We\'re getting pounded with notifications for sites being down for a minute. How do I set that for a minimum of 5 minutes? If our hosting server has a delay of a few seconds, I don\'t need to know about that. If a site is down for 5 minutes or more, I need to know about that.