Not sure what answer you're looking for. You could probably rush through in 45 minutes. *Edit* We spent around 2.5 hours and had to rush through a lot of it because it was closing.
You can probably get through it in an hour, but I would plan for 3 hours to enjoy all that they have. That includes time to eat.
On average say a leisurely 2 hours. Longer if you have ever been and stop to read about the animals and do activities, less if you have been there before and you are just going for an early morning stroll through a pleasant little zoo.
It took my husband and I about an hour or two to get through the zoo some exhibits we stayed at awhile longer and we also fed the giraffes and the birds too so it just depends how long you want to stay at any particular exhibit for.
It takes us a little over an hour to get through the zoo, unless we happen to catch a feeding.
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