I'm not quite sure if the above post is tongue-in cheek, but people can leave when they like. It's not a race. And trying to get 2000 people to go through those narrow streets and alleyways all starting at 8pm - well, good luck.
I usually aim to start between 8.30 and 9pm. That way, I try to save the annoyance of being overtaken by a load of fast people who, all too often, overtake too closely. I'm usually at the beach in time for lunch.