If you have questions just call. You don't want to be late. I was late for my JHU interview because I forgot to pack a tie, then had to go struggle through downtown baltimore in the morning the day after an ice storm to try to find a tie. Then the store opened 15 minutes late, then when I bought the tie the credit card machine went down so they had to hand-write everything. Then I couldn't find a cab very quickly. Then the cab driver took a wrong turn and got stuck in traffic. Then I got lost inside the hospital and couldn't find the path dept. I asked for directions but they sent me to the wrong end of the building. Luckily though my interview didn't start til 10am, so I arrived at 10:15 and they basically acted like nothing was wrong after I said "Sorry, someone gave me bad directions."
That's a true story.
Amazing how many things happened that morning, in retrospect. But the interview day went well.