It really depends on how in-depth and how interested you are in the exhibits. If you really take the time to read the signs and chat with the docents/volunteers then you can easily spend 3 days. If you want to just do a gentle stroll through the exhibits then 3-4 hours should suffice (excluding movie and visiting the museum store). As with visiting most museums, you do not want to rush through the exhibits since there is a lot check out and explore.
About 3 hours. Not counting if you watch the 45 min movie.
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