I say the idle effects should be consistent on when they start. I noticed Thor's Strike does not initiate as soon as Smoke of the Halloween idle effects. I suggest that all idle effects start at the same time. I would use Smoke or the Halloween Mask idle effects as a template. They start quickly.
I can't really agree or disagree...I never paid that much attention to the timing. I just noticed that Blizzard and Death Mist don't share the same flourish. Blizzard is clearly better. But I only bought Downpour because I like it more than the others. Now that I think about it, Darkness does have a slow start up time with pretty much all instances.