I've pitched dry yeast and had fermentation start within 24 hours and had good beer in the end.
I've pitched rehydrated yeast and had the same results.
But anymore I always rehydrate in water temps that the yeast maker states on the package.
I guess look at it this way, the yeast expert that packaged the yeast recommends it so why not follow the experts advice???
I also try to get that rehydrated yeast down within 10 degrees of the wort before pitching as well to keep it from getting shocked in anyway.
*** Possum Trot Brewery ***
Beer Primary - Butthead Belgian
Beer Secondary - Belgian Tripel
Bottled - Big Breakfast Stout - Belgian IPA - Butthead Belgian White - Redneck Red - Moose Drool - Dirty Dubbel
Mead Primary - Nuttin
Bottled - Strawberry Trainwreck - Orange Spice - Blueberry Trainwreck