How much time should I give to the zoo

An entire day.

Would say entire day. But if pressed for time then you can speedrun in 4 hours

All of it. It is beautiful

Minimum 4-5 hours, Recommended for a whole day if wish to complete the whole park

We spent the whole day.

We go often so we only visit parts at a time and usually spend 2-3 hours. If its your first/only visit you could easily spend 6-7 hours.

Min 6 including lunch breaks...

We usually do about 5 hours.

We were there 3 hours

4-5 hours