No, this is not appropriate for gnocchi; it will turn soggy and it will not be possible to return it to its firmer state. If you want to make gnocchi ahead of time, make the dough mixture ahead instead; it can be made the day before if it helps your dinner plans. Roll the dough out after making it and cut into pieces, then place into a storage container. Cover the container and place in the refrigerator until you're ready to cook the gnocchi pieces. Then, cook just before serving to keep the best light texture.