The Halloween event and West Coast Players
Daily quests and monthly quests end at 5 Pacific daylight time. We’ll still be on daylight on 10/31/12.
The yet-to-be-revealed event, let’s wait and see.
If the event timing is anything like how it was in GW1, then the event will end at midnight, (Actually, usually 12:01 AM on the 1st of November would be more likely.), on the 31st for PST.
Mind that this is based on my experience with similar events in GW1. Since ANet itself is West Coast to the best of my knowledge.
In GW1 they eventually made events run for a whole day every 2 hours or so, hopefully they learned and do it the same way here.