How to set external calendar sync period or force a sync?

[rsteiner]

I have users set up with a sync to external iCal (ics) calendar(s). I know in the Zimbra Web Client you can right click on the calendar and click Refresh. But my users find that a pain to remember (and I agree).

I haven't been able to find where I might set the sync period for Zimbra to update this calendar. Searching the forums it appears this time is 6 hours. I'd like to get this down to 30 minutes to an hour. If there isn't a way to change that setting, is there a way through an API (or SOAP call or whatever) to trigger Zimbra to refresh/resync to the external calendar?