Clarify the relationship between [start not before] and [start time] and sort out the state diagram accordingly:
- [start not before] feeds into [start time] attribute.
- if [start not before] is *not* set, [start time] is not set and the DTI instance sits there waiting forever, waiting for either the "start()" 
operation invoked (or until the system policy cleans it out according to [end no later than]).
- if [start not before] is set, [start time] must be set to the same value, and the transfer MUST start automatically at that designated time in the 
future.
- Users MAY start a DTI with a [start time] set prematurely.
- Make [start time] optional in the instance attributes document