It turns out that Daily Notes, Day Events, and Holidays all get the same treatment from the CAPI export process, so I need to rewrite the iCalendar output for all of them. Instead of using a DURATION to these events, I ended up just removing DTEND. Thus we end up with an event with DTSTART but no DTEND, which iCalendar defines as an event that takes up no time. That’s pretty much accurate, except in the case of Day Events, which technically take up all day. Unfortunately, in Oracle Calendar, some people put entries in as Day Events when they really should be Daily Notes. For that reason I’m not quite decided yet as to whether I should put DURATION in for Day Events. In any case, I’ve fixed the problem, and everything shows up in PHP iCalendar. For now I’ll just leave DURATION out, until I change my mind.
One thing I might consider, is splitting the four Oracle Calendar categories (appointment, daily note, day event, holiday) into separate calendars, so I can differentiate the various events more easily in iCal and on the Palm. It seems like a good idea, but will require some extra work.