Failing to pick up all of the fallen blossom and leaves from Quince trees will do no great harm, so if some are nibbled during the short season they are on the ground don't worry, but don't offer them as a part of the diet.
Also,as they get older and wilt, the leaves produce a cyanic compound, so it is wise to try and remove leaves that might fall into the tortoise enclosure if possible (although tortoises might ignore them as Quince leaves contain a high level of tannins that give them a bitter taste).
The seeds of the Quince contain hydrogen cyanide, which is poisonous and should be avoided. The flowers of Quince are white tinged with pink but closed buds show mostly pink. Do not confuse with Flowering Quince. See also Quince (Fruit).