My petitioner has felony case. can this be a delay to our usa fiance visa? how long?

if this is all there is to it, it will have no impact on your petition. they would only be concerned if this was some sort of ual crime, or a crime of violence directed towards women or children. they are much more concerned with your police record, so if you don't have one, and you can show a real relationship with your fiance, you'll be fine.