The starting young waterfowl handout that I got from Dave Holderread (author of the Storey Guide to raising ducks) last week when I picked up my new babies states that the temps should be:
90-92 degrees for the first 3 days
85-90 for days 4-7
then drop the brooding temperature approximately 5 degrees each week.
Storey's Guide says 85-90 for the first week, then 5 degrees less each week.
My brooder was initially 92-93 degrees, it is now 88ish and the babies are 5 days old. The ducks stay right under the light, the geese hang out at the other end about 1/2 the time and are under the light sometimes too.
Make sure there is room in the brooder that they can get away from the heat if they get too hot.
Good luck with the hatch!
My ducks usually don't need as much heat, or as long as chicks do. However, I do make sure it is plenty warm after they have baths so they can warm up and get dry. What raindrop shared is pretty much the guidelines I use. The ducks will move in and out of the warmth and regulate their heat themselves, if they have enough room.