I went in the other direction: starting in Newton and going out in the southbound direction and back in the northbound direction. I started just before sunset and navigated by headlamp for the first few miles until the rt 9 crossing. There was a bit of extra mileage, usually caused by poor signage on the road portions. I have never run the southern half before. On the return trip, I had a little trouble navigating in Chase Woodlands. I ended up back on the trail going the wrong direction and more than made up the distance. Fortunately I recognized sooner rather than later that I was going south, as I remembered jumping over a fallen tree in a particular way on the way out. The outbound trip should also be a oneway southbound FKT of 2h 22m 09s. The effort was unsupported. It was hot and I carried about 20oz of water and 10oz of Gatorade. Here's a tip (more helpful in the other direction), there is a water fountain that works in Oullet Park in Wellesley.
out & back
4h 59m 32s