ZooAmerica is a walk through zoo and is part of Hersheypark. As a North American zoological exhibit, you will see plants and animals that are native to North America (no monkeys or giraffes)
According to their website (which has quite a bit of information, by the way) the park will take about an hour to tour. There is no time limit however – and you can take as long as you need to explore the zoo.
ZooAmerica also suggests that you visit in the cooler months and also in the morning – as the animals are more active.
Visitors to Hersheypark can enter ZooAmerica at no additional charge.