Hearts will never have a better chance of beating Celtic in a cup final....but they have to score first and as late on in the game as possible.
Celtic look to me to have turned a wee bit of a corner recently. They were much improved in their last Europa Cup game and also last week-end. Their scottish players as usual are the ones who are getting them out of a hole. However they still look very shaky defensively and Hearts have got experienced players like Naismith, Boyce and Walker who can exploit weaknesses and cause them problems, as well as couple of fast wingers.
Celtic player for player are just on a different level though, and if they play to form and especially if they score early, they will probably win comfortably. The longer it goes on at 0-0 though the better the chances for the jambos. I wouldn't rule them out.