I think we have to make an important distinction between condemning the parent and acknowledging the truth that all people are imperfect. Imperfection does not equate with condemnation. If you are able to see your parent as imperfect, then it follows that he or she will sometimes make mistakes or even do wrong. You can then forgive while you keep in mind that this is not condemnation or disrespect. In fact, it is an attempt to see your parent as possessing inherent worth despite the imperfection. To me, this is a sign of respect for the parent as a worthwhile person.
The deeper the emotional wound, then the longer the forgiveness process seems to be. In a case like this, yes, it could take many months for the one who forgives to experience emotional relief and to conclude that he or she has forgiven. Please keep in mind that the one who forgives does not have to become a perfect forgiver to experience emotional relief.