I think being able to forward-guess exactly when Hanoi's leaves might be turning is impossible. It depends on what the weather patterns are doing both temperature and rain-wise. And in some years, might not really have much of a colorful presentation at all, will go from green to brown then fall quickly. I've been in Hanoi in October and November during relatively cold years, and my experience was the latter--very little color. It's not like trying to time the leaves in Vermont, which is fairly predictable.