Monitor alerts are delayed?

I've been seeing this recently, where we have monitors setup for service restarts or low-disk space alerts.  For example, this morning, we received an alert for a server that was low on disk space...email came in at 9:05AM, Date/Time stamp on the alert was 9:03AM.  This is fine.  However, at the same time I received an alert from another server...email also arrived at 9:05AM, however the Date/Time stamp on the alert was 7:18AM.   Similar issues with expected service restarts yesterday evening that were showing up an hour after they occured.  Obviously this causes a problem for any troubleshooting if we're not getting the alerts in a timely manner.  Nothing has changed recently...no new monitors, no server upgrades, no software upgrades.   Can anyone point me in a direction for troubleshooting?  Thanks!