Maura left Amherst Mass. just before 4:30 pm according to all info there is out there. We have no way of knowing that is 100% true but must be close because of the time the Saturn was seen @ the Weathered Barn corner. The trip takes about 2 1/2 hrs going by Mapquest.
So…….If the Saturn did leave right at 4:30 it is completely possible for the vehicle to be there for the 7 pm timeline, a first accident minor and the eventual spin out at the WB corner.