Groups are required to have passes every day during peak and off-peak seasons.
Not necessary but a good idea as they try maintain crowd control.
You can do it on sight too once you are at the door they will tell you how you should do it.
You can go on the website starting @ 6:30 am to request timed passes. I believe the max you can do at a time is 6 so if you have multiple adults you can each request the timed passes. Theu have group passes as well you should contact the museum directly for that.
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