We were there for 6 hours. There is a lot to see. If you are just visiting the zoo, I'd say 6 to 7 hours. Also, week days are less busy and that's when we went. If you go on a Friday or weekend day, it will be a lot more crowded. One more idea, we repurchased our tickets online and saved $10 bucks off each ticket.
Starts emptying around 8pm. Many stay for the parade at the front that starts at 8:30 then leave.
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