On the iPhone you can create an event and set it to alert at the time of the event (as opposed to x minutes before)

If you do this though when it syncs to Zimbra the reminder is blank. After a while on the iPhone the alert becomes 13,730 days, 22 hours, and 4 minutes before the event!!

I guess this is a bug, was just wondering if anyone has a workaround apart from alerting 1 minute before?