Build on the connection you’ve already established – send that revised dummy to your art director contact. Five months is fine as long as she put no time limit on submissions from that conference. I wouldn’t even give it a second thought before six months. An explanation is in order, though, if you take longer than six months. At a year, you’ve pretty much missed that boat. The art director may question your ability to produce in a timely manner, or she just might have left the company altogether. There’s a lot of house jumping in publishing.