Does the air conditioner work? That's supposed to come on is defrost mode; the dehumidified air greatly aids the defrost process. Also, how's the volume of air through the defrost vents? The flap that diverts the air may not be moving properly. Finally, you should not have the "recirculate" button pressed - that cuts the efficiency of the defrost process quite a bit. Note that on my car, there are visible results in "defrost" in less than a minute.