This sealed class represents the different types of event time configurations.
Class representation of an entire day spans without specific times. Your birthday and holidays would be represented as date subobjects.
Class representation of a specific dates without clock-based start or end times. A business quarter or academic semester would be represented as datespan subobjects.
Class representation of a specific point in time. A meeting at 2pm would be represented as a time subobject.
Class representation of a time span with start and end times. An hour lunch meeting would be represented as timespan subobjects.
Returns the WhenType of this When object.