at least an hour
It depends. I suggest to take a picnic style afternoon over there by the lake that's right next to the butterflyworld. Strolling some hour and half watching the butterflies and birds (and some insects of you like) will be crowned by the picnic. If you have kids, there's a playground as well. Or, you can spend the afternoon playing frisbee-golf.
It took my wife and I about 2 hours. We went at a slower pace. I would plan on 60-90 minutes.
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