We started our road trip in Rhode Island, Massachusetts, from September 11 to September 16th. Sadly, at that time things were still very green. As we got closer to New Hampshire, 16-20th, things were taking on their autumn look and it was getting very beautiful. It was a very nice experience, and we got to see a variety of different colors. As for Vermont, I would say that the beginning of October would be a better time, because the colors were quite early in terms of changing.
As for Acadia National Park, even when we were there towards the end of September, only some trees were changing. The drive up from New Hampshire to Maine, it was probably on and off with some really beautiful colors, and then when we reached the National Park, it still hadn’t reached it’s full autumn potential. Keeping this in mind, I would definitely recommend going to Acadia around October.