Forgiveness is a choice not a feeling. Your feelings may not change while you are praying, but you can choose to forgive at any time. It does not take long to make a choice. How long does it take to forgive? How long can you stand and pray? Jesus never said anything about the person deserving forgiveness. Nor did He say to forgive only after they asked for forgiveness.  Anytime you talk to God, Jesus said to forgive if you had anything against anyone. That would include people who hurt you without even realizing they hurt you. Even people who were still trying to hurt you. "Anyone" in this verse includes everyone, no matter what their attitude may be. Why should you forgive them? Not because they deserve it. But because of the harm it will cause you if you don't forgive. The reason you are to forgive others is to maintain your status with God.
Jesus indicates there is something about us refusing to forgive others that hinders our relationship with God and the free flow of blessings God desires for us to receive. I understand that forgiving someone who horribly wronged you is not easy, especially if they are not even sorry for what they did. But Jesus makes it clear that you have no real option. You MUST forgive if you want God's forgiveness. I need not tell you
how vital that is. If Jesus appeared to you right now and asked you face-to-face to forgive someone who hurt you would you do it for Him? We should respect Jesus' Word just as much as we would respond to
Jesus appearing to us face-to-face.

“For if you forgive men their trespasses, your heavenly Father will also forgive you. 

 But if you do not forgive men their trespasses, neither will your Father forgive your trespasses (Matthew 6:14-15).