There's a piece missing here. Are you flying back to BOS on the same ticket?

If so, cut it as close as you wish. If you miss your connection, the airline will put you on its next plane to BOS that has space.

If not (and your wording makes it appear that this is the case), it's the roll of the dice. At this time of year, a snowstorm can cause delays of many, many hours. As I'm sure you know, such a snowstorm doesn't necessarily have to be in Boston to create havoc with flight schedules. If such a delay occurs and you miss your flight from ATL to BOS, it's up to the airline as to whether they will put you on standby for the next flight, versus charging you full fare. Most of the time you can go standby. But don't count on it.

Since flying DL from BOS to ATL is obviously one of the options you are considering, what's wrong with the non-stop that gets in at 12:03? That gives you a considerable margin for delays and doesn't leave BOS until 9:15, certainly not a ghastly hour.

Lastly, it sounds as though there is some possibility you will have overlapping flights on different tickets that could be considered by Delta to be back-to-back tickets. Be sure you don't run afoul of these prohibitions or you might find yourself confronted with an agent who demands a stiff price (full fare rather than your purchased discount fare) before allowing you to board a flight at any point on your multiple-leg journey.