Once you have a date, make the permit a priority.
You don't want to pull a permit too early, especially if dates are tentative, or the necessary research isn't complete. Just don't wait until the 59th minute. Be warned: It's easy to procrastinate on this.
The lack of a permit can bring the whole extravaganza to a grinding halt or provide a highly stressful sideshow for your participants -- and who needs that?
Most permits require 4 to 6 week for processing, while some permits can be done in 2 weeks. Just remember your lunch-loving friend at the permit office may not see your last minute permit needs as her or his top priority.