It is always free. The admission price is only a suggested donation, you can pay as much or as little as you want- including nothing at all.
The only thing that requires an obligatory payment is the exhibits... aside from those, just as Tim Barkus mentioned, general admission is based on whatever you can donate. The admission price chart only reflects a suggested donation. Again this applies to general admission NOT the exhibits. Those are full price unless you are a member...
It’s only free the last hour of the day. So after 4:45pm
Um it’s never free
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