The mini-evac will be done at night, in the dark, all lights on the tarmac off, to more closely replicate the conditions that would occur in a real life evacuation.
Figure the airport will generally be closed and most people will have gone home for the evening.
I would head over there after dinner, no earlier than 7:00 PM or so, and be prepared to hang out for a while.
It must be amazing to actually witness something like this.....a once in a lifetime experience......