Can I edit an appointment time or must I re-enter it
If you are talking about iOS appointment, there is a issue for editing appointment. There is an option called "Time Zone Override" in iPhone Settings. If user turns on this option, the edit event page displays wrong time or date. Actually this option for iCal, not EverCal, but it affects iOS's native page views like edit event page.
That's way we don't allow user to modify the event in EverCal. At this moment, the only way to modify an event, open iCal and modify an event.