I also cannot answer the question as my entrance was paid for by a private tour guide. As far as photographing the building, it's very tall and there are MANY intricacies that might be worth going in to photograph.

I found my pic on Tripadvisor. The performance times are 9:10, 10:00, 11:00, 15:00, 16:00 and 17:00. Be 30 minutes early as seats are very limited.

I thought I would follow this up... obviously I checked the various websites for this attraction and got contradictory information. That's why I was asking for clarification here. Anyway, I just got back from Xi'an and both towers closed at 18:00. You can still enjoy seeing them from outside and walking around the area, but to go inside, you must visit before18:00.