I'd probably use yeast nutrients, pitch a good amount of yeast based on Mr. Malty's pitching calculator and aerate the heck out of my wort just after pitching.
Quince is an apple-like fruit, and if it's been candied, then it might contain a little more fermentable sugars. I don't recall that it has a strong flavoring, so i'd probably add an ounce or two (you'll need to be the judge) into a grain bag and sink it into the beer just after primary fermentation is finishing up. Let it sit in the beer to taste, but if I had to guess, about a week.
Beer so good, it's frightening.
2014: Seven Heavens Series One: Vilon, Mystic Melomel, Skeeter Pee.