At my last position, we ran our exercises over a two day period. Two conference calls each day, one in the morning about 9am and the other in the afternoon about 3pm.
We ALWAYS invited the public sector (fire, police, FBI, etc.) to participate in the exercise. After the scenario and interjects were drafted, we would ask our public sector participants to offer suggestions/corrections. Then, during the conference calls, right after roll call, we would ask the public sector participants to comment on what would be happening if this were a real event. They would also be present throughout the day, if possible, to answer questions.
During the fourth conference call (call #2 on day #2) we would transition into lessons learned, again starting with our public sector participants.
This is a big topic, and I would be happy to discuss with you in detail. Please PM me with your contact information if you wish.