The fact is, we really don't know. We are coming out of "solar minimum" now, when most the storms are from "coronal holes", which are generally not major storms. The big flares that cause the massive storms generally occur around solar maximum, when the spots are larger and more complex. We get about 3-4 days once we see a major spot, then when it gets very complex and in a "sigmoid" shape, the flare may be imminent. The flare can send energetic particles and launch a CME. The CME will take about two days to get to Earth. (See my keynote talk from yesterday).