Suppose that User A invites User B to a meeting, and User B hasn't responded yet.
Now suppose User C wants to invite User B to a different meeting around the same time.
What I seem to have just observed is that if User C is using ZWC, then User B shows up as tentative in the Schedule tab of the Appointment.
If user C is using iCal 3.0 (with CalDAV), then User B shows up as busy in Available Meeting Times.
However if user C is using ZCO, User B's status may or may not show up as busy. If it doesn't show up right away, it seems to appear if you wait a while before creating the meeting.
Similarly if the original meeting (A with B) is cancelled, then User B's free/busy status is updated right away with ZWC and iCal, but User B may still look busy to Outlook for a while.
Just now it seemed to take about 14 minutes, while I was trying all sorts of things including closing/reopening Outlook (and deleting a local failure notice which was an hour old, seemingly not related).
(Note that User C is clicking Send/Receive in Outlook before creating the meeting, to make sure everything is synched up)
Have others observed this?
What exactly is causing this? Any way to control how rapidly the free/busy info updates for the benefit of ZCO? It is apparent that ZCO uses a different facility (the Internet Free Busy search field buried under Tools>Options) than CalDAV or ZWC.