Okay, it still takes about 8-12 hours minimum (24 hours at 55-60 degree room temps), but the first batch tastes good, which I've never achieved with my previous versions of making clabber.
I used 1/2 cup cultured buttermilk to 1 quart of skimmed raw milk...since the buttermilk is the culture, this could be made with pasturized/homogenized milk as well. I just whisked them together in a jar, put a clean washcloth over the top with a rubber band to keep the cover on, and put it on top of my refrigerator. In 24 hours it was as thick as yogurt.
When I want to make it up quicker, I have put the jar in a saucepan full of hot tap water. It then thickens in about 8 hours with my changing the water a couple of times. It would probably thicken more quickly if the milk was warmed before adding the buttermilk, too.
I've been using that original quart to culture clabber for the pigs and chickens (about a cup to 3 gallons of milk), to culture cream for butter making (yum!), and for cottage cheese. I'll soon culture another quart of milk to have an on-going starter.