A full day. Go to the zoo first and then head to the aquarium when it is hot so you'll be in the ac. Also animals aren't as active when it's hot.
I wouldn't rush either. But I would start at the aquarium at open and then go to the zoo
If you take your time in can be done 3-4 hours of rushing it 1-2 hours
I'd say a good day at the Zoo, Aquarium and Botanic Garden takes me and my family about 2-3 hours. We eat there also.
I also agree with Tc axtell! Get started as soon as the doors open for the zoo, botanical gardens and aquarium, relax, enjoy.
If your rushing you can do it in the day. However i suggest the zoo one say and the gardens and aquarium the next.
All day
I did the zoo first, then the aquarium and the gardens which I ended up being glad I didn't skip (esp. the bugs). I noticed many animals (chimpanzees for example) became a lot less active once the heat set in so I would do the zoo first.
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