What is the purpose of this property?
I was under the impression that it might be used to indicate that an event extends across the whole day, that is, from 00:00 to 23:59 (or from the open hour up to the close hour).
But if I don't supply a start time and end time, nothing is shown (if I leave out the end time, the duration is that of a single slot located at the specified start time). And if I have to supply a start time and an end time, that kind of defeats the purpose.
What am I missing?