The fall months are a good time to plant. Just remember to mulch well and maintain the soil as constantly/evenly moist as you can (water only once every two weeks when the plant goes dormant if winter is dry & the ground has not frozen). If we are talking REALLY young plants a few inches tall then I would bring them into the garage when dormant, water them there once every 2 weeks and plant them in the Spring.

If the ground is frozen, it is too late to plant. If it is not, grab a shovel.

The technical answer is that you get the same amount of root growth from fall planting in six weeks as you get from planting right away in the spring.

The practical answer, especially in such a balmy clime as Mass, is that if you can put a shovel in the ground, you can plant. If it's really close to ground freeze, or if the frost thaw cycle in your ares is prone to cause heaving in small plants, put some extra mulch around. And leaves work.