15h 37m 0s
I started the gps at each trail head, I chose the most direct way up each mountain.
Mt Washington via Tuckerman's Ravine (3h24m25s car-to-car)
Mt Mansfield via Laura Cowles (1h41m39s car-to-car)
Mt Greylock via Thunderbolt Trail (1h37m30s car-to-car)