Firstly, keep your forehead protected, in its weakened state, your skull will not be able to protect you from brain damage.
Secondly, because of its area, and its shape, its hard for it to heal like a long bone (aka femur (leg bone)). It can be from 8 weeks to several months before it will start to build new bone in that area. Just take it easy and try not to put too much stress on that area