Actually, I believe that others can piggyback much earlier than 30 days by filing a piggy-back 211, but they've got to file within a specific timeframe. After 30 days all that is required is permission from FINRA, which evidently is a very simple process at that stage of the game.
All of the above I learned on the SLON board during its very long 30-day wait, so it might not be completely accurate.