Also, flights out of B tend to board a little later since the aircraft are smaller capacity RJs (i.e. often board 20-25 minutes ahead of departure time rather than 35). And when I have a tight connection to B, I generally find the G/A standing there with the list of missing pax and their inbound flight info on screen. If you're the last one, they'll even call you by name as you approach.

But, yeah, with such limited alternate connections, probably good to take the earlier flight out, which, as someone pointed out, they should let you change to for free given the change in your itinerary.