C2MS11 — Time Type table clarification for the DDD portion

Document clarification: The DDD portion of the Time Type, as shown in table 8-2 on page 40, has a range of 1-365 (or 366). But when using a relative time (by preceding the value with a "+" or a "-"), the DDD portion can contain a zero value. Make this clear and add a couple more relative time examples.

Consider replacing C2MS invented date format with RFC3339 or ISO8601 to include relative time.