I apologize if this aspect of siege has been covered, but in reviewing past requests and fixes for the siege auto-start it looks like this piece was overlooked.
It appears as though the act of initiating the new game, or creating the game instance has been resolved and they now autostart or are at least start-able by either the defender or the challenger.
*** The part that is missing is that a defender can't force the clock to start, because it is dependent on the first move of the challenger playing the white pieces. ***
The only argument I can see for this is that the challenger should be made aware that the game has started. But I'd retort that it should be just like a tournament where they get an email (if settings permit) and then the game is off.
Also, by adding your name to the queue, you should be acknowledging that you are 'preparing for your attack' in the act of monitoring the progress of the game(s) in front of you so as not to be caught off guard.
It should not be possible for someone who has dropped off the map, for over a month, to hold up the queue indefinitely, even if unintentionally, as is the case with the current application of siege game activation.