Emotions will dissipate as quickly as it takes for the biochemistry to re-normalize. If the provoking thoughts are not set aside, the emotion will remain. Yes, forgiveness should not depend on the repentance of the offender although it may help. You can forgive someone, but it doesn't mean that you have to like them. I think that dislike is an inseparable part of the unforgiving state. Therefore, forgiveness should include the absence of dislike but not necessarily the presence of like for the offender.