Sorry that my post is late this week, I hope you've had a great weekend :)
If you are planning on visiting the zoo I would recommend booking online, you have to pick times to see the pandas and they go very quickly, I'm so thankful I booked in advance or I would have missed seeing them as the time slots were rammed. After all the travelling I would have been devastated. Even though you have to book a time slot the viewing is free so don't worry about extra cost which is good, when I went to see them they were sleeping so I'm glad I didn't have to pay extra! Also, if you have a smart phone or iPad you can jump the queue on entering the zoo with a barcode that they send to your device - great time saver.