I don't think they did, and I don't think you did (please read my tone with generosity; that's not meant to be an attack.) I don't believe the feedback they go

I don't think they did, and I don't think you did (please read my tone with generosity; that's not meant to be an attack.) I don't believe the feedback they got was that they should be charging, and they aren't yet, therefore "the best time to plant a tree..." The question they got was "Why aren't you charging yet?", because by product and market, it seemed they ought to be. The correct answer is "This is our market, this is our business plan, this is why it makes sense for us to not be charging yet." The question is one of rationale, which could be judged as being good or bad, but still the question is "why?" Their actions revealed that they didn't have a solid rationale. So without any more reasoning than "because it seems like YC is criticizing us for not charging," they quickly started charging. Did YC's criticism actually change their business strategy? Their knowledge of the market? Anything that should have plugged into the question of whether they should be charging? If the answer is "no," then they launched a significant change to their product without any good reason and, in my opinion, validated YC's opinion.