Time Span
This contains a Start Time and a Duration.
The Start Time can be defined up to one of the following resolutions:
The Duration is specified by a single number whose units are one of those in the above list.
A Time Span can be used either to set a Start Time and Duration (e.g., setting the values in a particular ERF before doing a hazard calculation), or it can be used to get the values set by someone else. The creator of a given Time Span can specify what range of Start Times and Durations are allowed (e.g., so the devloper of an ERF that makes only daily forecasts can prevent someone from setting the duration as 50 years)
A Time Span can also provide the End Time associated the Start Time and Duration (and thanks to Java's GregorianCalendar implementation, all leap years and seconds are accounted for).