You actually have two questions here, not one. 1) The title refers to the minimum time to connect. 2) Your last sentence asks how much time you should realistically allow. These are two different matters. You have already received much helpful advice, so I will just add one further consideration. Much depends on the time of day you will be flying. If you are connecting to the last ORD-BOS flight of the day, failing to make the connection will have undesirable consequences; if you're flying earlier in the day, the inconvenience may be slight.