How to customize an event notification

[sdao]

I have an issue with our CPUs monitoring. The CPUs (#2 & #3 of 4 CPU) on one of the node in a 2-node MS cluster keep hitting my critical threshhold of 98% then drop back to normal within a few minutes span, I receive an email every time it hit this critical threshhold.
How do I customize the Event Notification so that I only receive email if one of the CPU hit the threshold and STAY THERE for 5 minutes ?
Thanks
Sonny