Hmm... Since I have kefir grains and am playing now with pizza-making, this thread looks very useful.
A bit more about kefir as such. Basically, the time for it to get ready depends on three things: temperature, the amount of kefir grains relative to the milk, and whether or not you mix/shake/agitate the kefir as it matures. This summer was hot and I had problems with kefir being too quick -- now that it's fall the whole thing became more manageable. I set things up so that my kefir cycle is 24 hours -- it's very convenient. To achieve that at my room temperature I use the proportion of 1:10 of kefir grains to milk and I do *not* agitate. My milk, by the way, is regular store milk.
Note that (from my point of view, at least) the kefir is NOT READY YET when you separate the grains from the kefir. I put it into a container and it goes into the fridge where it continues to develop for 24-72 hours. The longer you leave it, the more sour it will be. For my taste, 1-2 days is about right.
Kefit left too long will separate into curds and whey. You can make sour-ish cottage cheese out of it.
I'm still too much of a newbie to play with kefir starters, but once I get my standard pizza routine down pat, I'll start experimenting and will definitely explore the possibilities of making kefir-leavened dough.