There was another thread on this topic, which pointed out that they do this right at the official sunset time. This surprises many people, because it's still very light out at sunset -- sunset is long before dusk.
Anyway, if you go here:
http://www.timeanddate.com/worldclock/astronomy.html?n=783&month=10&year=2012&obj=sun&afl=-11&day=1
you can look up your dates and figure it out. It looks like, for middle of October, sunset is right around 6:15. I'd get there by 6:00 to be sure.
-Bob
Thanks Bob!
