Reading the question, I thought the answer was six as well. Such a question is so misleading that I would hope that an AI answers as it has in this case, because not all problems are fully logically specified, and you need to remain robust against the question being posed incorrectly.

In other words, I would posit the probability of you having meant for the answer to be 5 low, because the question itself becomes trivial. For a system that needs to deal with many people asking questions, this robustness is helpful in my view.

In other words, it's not totally clear that time has not passed between sentences in your prompt. So the second instance of "now" could be a different "now".