Slow growing starter

I am making a rye flour wild yeast starter using the instructions in Reinhart's Whole Grain Breads. My first attempt never seemed to work so I discarded and tried again. This time it was quite active until I got to the point of converting my seed culture to a mother starter and he says the rising here (to double) should take 4-8 hours but mine is growing, but it has been more like 24 hours and it is still not there. I'm not really sure what to do.