The thing about the calendar is...if used properly (and somewhere there's a post), the calendar shows you the correct date and time according to your own time zone settings.
So a GM in one time zone can set up a quest, and anyone viewing it will see the date and time translated to their own time zone. So in effect, it should be very not confusing. This is in contrast to the old forums, which had no such facility and we had to rely on GMs doing time zone math...which is just frightening.
Having said that, I seem to remember the calendar having some kind of odd issue with Daylight Savings Time, but I don't recall exactly. Again, there's a post somewhere.