Heat the water to temp THEN put in the specialty grains. It's the same idea as making tea or coffee, you want to extract the color and flavor from the specialty grains, and 155 is the optimal temp to do so. As close as you can maintain the temp at 155, the more consistent results you will get, though it's not a big deal if you lose a few degrees or overshoot by a few.
The magic BAD number is 180F, as prolonged exposure above that temp with help from proper PH conditions will start to leach undesirable tannins into your wort. Don't think of tannins as that much of a boogieman, though, because lots of peeps, including myself, have accidentally boiled, as in 212F, specialty grains for 5+ minutes and had no problems with tannins even at that temp, as the PH conditions really need to be spot on to aid in tannin extraction as well, and they typically won't be in your extract batch unless you are actively trying to control PH with water conditioning agents.
Anyways, all that to say, RDWHAHB!!!
Good luck!