I have spoken to everyone I can possibly think of, more than once. I know I'm supposed to wait at the apiary in the evening. When nobody showed before midnight, I checked the walkthrough, but I can't find anything I did wrong, and still nobody is showing up to burn the place. Please help!

You do not need to wait till evening. You can met the instigators in any time in that day. They should be between the two blocks of the apiary, in front of the main entrance to the abattoir.

I just got home an hour ago and tried something that came to me on my way home... it turns out that if you're flying, you can't trigger their appearance. As soon as I landed and walked normally a bit they showed up right away! *embarassed* I haven't really cheated in any other way, I've just been finding myself pressed for time, and flying makes things much faster over long distances. I hate walking clear across the town through infected districts >.< Thanks WhiteWind! ^_^