Is November too late in the season to top 2-3 ft off an arborvitae hedge?
Arborvitaes are good as hedges when you let them grow their natural height and only prune lightly. If you wish to grow a hedge to a lower height, then you need to select plants that can be topped heavily or only grow to the height you wish to have.
That being said, Arborvitae should be pruned when dormant, not during the active growing season. By topping the plant after it matures the growth at the top will not be attractive, since it will not send out new growth.