The contact will be unblocked immediately. Now, make sure that you are a hundred percent sure about the contact before unblocking him/her. It is always better to be safe than sorry and in matters of digital privacy, even a single percent of doubt is enough to keep unwanted contacts blocked.
There are many apps in the App Store and third-party websites, that claim to handle these operations for you, but we request you not to download such apps as they cause more damage than good.
