I don't know the answer to that question, but (zone 10 ) my tree ripened in December and held its fruit to late January. The fruit started getting very ripe, probably overly ripe, the color of the fruit almost became orange, or at least a very orange-yellow, and the peel started getting noticeably loose.
The fruit start getting more sweet, and somewhat less sour, when they are overripe, but they also start becoming a little dry inside. It's not a fruit most people would want to eat out of hand anyway, so there's no point letting it get overripe.
I know that Nanshodaidai (C. taiwanica) can stay hanging on the tree for a very long time, maybe almost a year after they are ripe, that's in fact where the Japanese name derives from. (Though that variety is more ornamental and has worse taste than Yuzu)