That completely depends on what you want to see. I have walked there for five hours, taking all the little trails through various sections. Like Michelle and Vicki says, it depends on what you want to see and how much time you're willing to take seeing it. I will say it's nice to build-in time to sit and relax on a bench or just pause and admire some of the art work.
Best to look at the map and decide where you want to visit. Even the butterfly enclosure can take some time but is next to the main building so could start there if your time is limited.
That call depends on how fast you walk, how long you stay in different places.
When we go we usually spend 4 to 5 hours but she likes to stop and look
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