The fruit leather update:
It worked! I transferred the quince leather onto a drying rack and let it sit on the stove and come morning it was tough, chewy, and delicious. more than 24 hours of drying - but it worked. Next time I'll definitely use red wine and I'll remember to turn the fruit leather over onto a drying rack, NOT back onto the cookie sheet!
I'm going to freeze part of the leftover quince butter to use like jam and use the other part for a quince cake (the kind with the fruit spread between two layers of dough and baked in a bunt pan. Yum!