For example,San Diego Zoo is open from 9AM until 4PM- Current Hours; Summer Hours are from 9AM- until 8PM.

Zoos have different times for each place to open, like the San Diego Zoo would close at a different time, then the Dallas Zoo, most of the time the Zoo is open from 6AM until 6PM, Holidays and Sundays are different,from 10AM until 6PM or 10AM until 8PM.