Rajah's right mate - the sun spot has to cough up a big juicy plasma sneeze first
theres a lot of variables Ken, i'm not fully sure of it all enough to explain it properly. I just go out when the odds are good, and if you get lucky, you get lucky if you know what i mean. Not all sunspots create CME activity strong enough to cause aurora to be seen at our latitudes. if there is one, and it is pointed straight at earth at the time, it can take anywhere from roughly just under 24 hours to 48 hours for the leading edge of the plasma cloud to reach earth, and can last up to 48 hrs in duration sometimes, if it is big and dense enough, but that isnt common, usually 24 hrs at most ,before it has fully past. The speed it reaches us at is very much determined by how big the flare is measured to be - a strong X class (the highest) will get here faster than a M class generally.