I don't have UFO's. That makes them seem like a lost cause. I call them "WIP" -works in progress ! Ive had projects for several years or more that were unfinished for one reason or another and I have picked up some again and finished them. So I say - no time limit. If you really hate them, pass them on to your quilt guild. I'm sure someone would love to have your project to work on! And if you are just frustrated or tired of it for the time being - just bag it up. Your skills will get better and your patience will increase and you may finish it at some point.