They actually are clear on the event times now, they start and expire at 5am France time, which is when the daily missions and pvp bonuses reset. The only confusing thing is that I didn't realize France starts DST about a week earlier than the US.

Drop chances are really low. I've gone through all three runs of the original Halloween event without getting that version of Juliette, though I've been lucky to get all the other non-legendary troll girls.