It is okay for certain parts of your head to dry faster than others and this is typical. You will most likely always have the top of your head dry quicker than the ends and bottom layers as all the moisture tends to trickle downward and these hairs aren’t as exposed to the air or absorption materials as those on top are. Also, you have to factor in the head coming from your head as well. The goal here is to have the entire head dry at the one-hour mark. Keep in mind that it is very common for the top layer to be more damaged than the rest as it is the layer most often exposed to UV rays, friction, pollution, products, etc.