Source: Rex Saffer (saffer@stsci.edu), r.b.c., 3/27/95
In my experience, the Yeast Labs cultures take a day or two, sometimes longer, to get going, but once active, they propagate in less than a day. If I can't brew when they are getting ready, I just pop the starter with its airlock affixed in the refrigerator until I have time to brew. I like to make several batches from one culture so as to spread out the higher cost of the liquid yeast.