Attitude - humble, greatful for the interview - always works pretty well.
Don't downplay your college, lets 'em know you are able to keep up with the courses, they should be academically fairly easy for you. but don't tell 'em you're a genius and they should simply open the door for you either.
Trust me, you're about to have your eyes opened that not all truly intelligent people want to wear a tie and Brooks Brothers, and some of 'em don't mind mud, cold, heat, and sweat.
Let 'em know that while your original career was interesting, it's over. You're ready to actually build something with your hands that will stand for years. You're ready to join a band of brothers (Union and open shop) who can say with pride they were there to make it happen.
Believe in an attitude of service, and the dignity of work, you'll be fine, and that don't necessarily apply just to 'lectric work either.
They want someone to show up, and produce, AND do a good competent job. I would not needle them with "how much time off?" questions at this point, if you've been unemployed, take the danged job, give it some time (sorry, unless you live in Nirvana, the FNG's ALWAYS catch crap) and look around, you're about to join something truly amazing, making friendships and memories you'll never lose no matter what happens......... some bad.
Don't be a minuteman, either to the interview, or after, NOTHING is more irritating to a boss than someone who just barely makes it on time, be a few minutes early to the job, have a cup of coffee with the crews, you can learn a lot that way......... AND get coffee.
Boss' and foreman are different, some are a PITA, some are golden, take 'em all in stride, I learned a lot from guys no one else wanted to be around... they were still a PITA of course.
With your education, it may be that fire alarm tech, or some such, is in your future, a little easier than general work, but you may find you like the general stuff to, give it all a chance.
Good luck, we're pulling for you.