I always fly in the day/night before, and leave the day/night after. It's worth it for me to see not only the campus, but the surrounding city, as well. Also, it's always a hassle/time crunch having to check out, bring your luggage to the school, ask to store it some place, and then head to the airport ASAP after the interview. I'd just rather spend the extra night. Almost everybody at my interviews, however, flew out the night of the interview.