Most dogs don't like to be blow-dried at all. If it's OK for your dog, set the hairdryer to lukewarm at most and keep one hand on the coat so you can tell if it's getting too warm.
Remember that dog skin is very sensitive to heat. If your dog dries very slowly, e.g. because he has a very long or thick coat, a dog bathrobe is a good idea.
Caution: Dogs do not necessarily withdraw when something becomes too much for them. Fearful ones in particular may endure the treatment stiff as a board. That is not a good sign. The dog is overstrained.
Therefore: Stay alert and watch your dog.