Sat Jul 04, 2015 3:07 am last year and ending July 29th.
acording to
viewtopic.php?f=2&t=43224and
Mon Jul 07, 2014 2:49 am the year before that and ending July 27th.
acording to
viewtopic.php?f=2&t=41259so my bedst guess is it will proberly start sometime in the weekend or monday
but could be wrong.....
just from those 2 post we can conlude it not a fixed date, and the event last around 3 weeks +- a few days
so no real hurry, it starts when it starts, and you should have plenty of time to find some NPC's even if you "mis" the first few hours.