Used it for the first time a couple weeks ago. I did the rehydrate method and fermentation signs began appearing at around 12-14 hours and then it just took off. From what I read before using this yeast (cannot personally vouch for the accuracy, its what I read), if you just sprinkle, plan on 24 hours (or more) before seeing fermentation activity. .
I've done it both ways in the last month. I rehydrated in a water with a teaspoon of sugar dissolved and let sit a few hours before pitching and +12 hours it was going good and in a full force at +18-24 hr. This weekend I just pitched dry and at +12 hr is was just starting and did not reach full force until +24-30 hrs. Incidentally, I did a 10 gal batch split between two carboys, one with Notty and the other Wyeast Denny's Favorite punch pack. The punch pack batch was going strong at + 12 hr while Notty was just getting started.
I have always rehydrated Notty.(Not saying its the "right" way just the way i do it ) Fastest I had fermentation was 4hrs. Id say 12 is normal. Make sure you use a blow off tube. Notty is a mad man