AH HA - this is what I have been seeing. It seems that what they said in the keynote and the intro videos isn't quite what is really happening. I don't mind a 15 minute window - I just want to know what to expect and I was expecting what they showed in the keynote and video.
Looks like one of the updates in 10.5.6 addresses this concern:
* Contacts, calendars, and bookmarks on a Mac automatically sync within a minute of the change being made on the computer, another device, or the web at me.com.