I have gone only once as a tourist. Spent 3 hours, paid as as I like but didn't went to see the exhibits. What I do recommend is to separate an entire day and be in line 15-30 min prior to opening. Once your in, start from the top floor down. (It will be crowded on the 1st floor when people start entering) This way you can enjoy everything on your own time and pace. If your near the area, you can always get a map and plan ahead with your luv ones. Hope this helps.
There are enough of them that you can spend your entire day just seeing the special exhibits. I would just say that if there is one that you most want to see, go to it first, because as the day goes on, it is only going to get more crowded.
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