You deserve credit for making something that's so authentic to the original. Really, it works just as well as does in real life. That's one reason I couldn't play this well. It took me like an hour to finish one of these in real life! I appreciate the overall design, but it could have used sound. Of course, a game of sudoku probably doesn't need it.
I guess there's no real time limit. It would certainly be nightmare if there was. At least I know how to play this game unlike Mahjong. Well, I kind of do, but I'm never good at it. You could probably use some better things here and there, but it doesn't really matter.