We went through the aquarium and most of the museum in about 3 hours. We pretty much took out time and even stopped for popcorn in the middle
We went for an hour through the aquarium/fishing museum part of it. I would bet the other half of the taxidermy side is another hour or two depending on how fast or slow you walk through the exhibit
I would plan on at least 2 hours for the aquarium part why go and rush they have benches so you can set and watch some of the biggest tanks it is the best way to really see the fish
Aquarium and museum would be 3-4 hours as long as you aren't rushing through it. The two are separated so you can easily take a break between the two. We got lunch and came back, just keep your tickets.
I'd give yourself a couple hours at least.
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