I'm a Southwest pilot based at BWI and A1 and B2 are the closest of the A and B gates. The farthest apart are A10/A11 and B15 and normally we plan on 20 minutes to go between the two. If you want to be comfortable with a connection at BWI, especially if you have an A boarding pass for the 2nd flight, I would plan on a 45 minute connect at BWI. That would allow you to go between the farthest gates and be there for boarding 25 minutes prior to departure. A 30 minute connect will still make the flight, you just will be boarding with the Cs.it is not unheard of to have to go from A1 to B2 which is about as far of a connection as you can possibly get at BWI.