Personally I plan to get there with an hour to spare maybe more. As for where the queue will be located, I'm not sure, Tobacco Docks has loads of entrances although I know a few have small shelter near the entrance, like a canopy type of thing. I think an umbrella wouldn't be a bad shout. An event I attended there before did have a cloak room provided but I don't know if we'll be granted access to it or not.