Date for returned list of positions.
This property is optional. It must be specified when IncludePositions property is set to True. If it is not included with the request, the server should return the most current position information available.
All input dates should be entered in the format specified by DateFormat. For example, if the DateFormat is set to "MM/dd/yyyy hh:mm:ss" (default value), an input date should look like: 09/30/2009 12:00:00 AM.
This format specifies also how the returned dates are going to get parsed.