I'd suggest posting this in the New England forum, you'll get a lot more responses there.

If it helps, I generally find that coming from Europe to the U.S., I'm very comfortable with 2 hours. I can often make the transfer in much less. But I've not re-entered the US through BOS myself.

Remember, your incoming flight may be late, and I assume there are limited options from BOS-CHS in the evening, which may be full flights. So you may want to allow some cushion to avoid a mis-connect.