Making sure that your servers time are in sync is important. You can verify the time with zabbix quite easily.
I created a trigger under Template_Linux (can also be set on individual hosts) with the following information (Do not copy the “'s!):
Name: “Time more than 5 seconds off”
If any of the servers are more than 5 seconds off the Zabbix server's time it'll trigger. The 5 can obviously be changed to any number you want. I might bump it down to 1 or 2 and see how that goes.