Yes
You must buy tickets in advance, if only because it is so popular. So far the show's stay in LA has been extended a couple times, but it keeps selling out so I wouldn't assume tickets will be available when you want to go, or that it will continue to be extended.
I don't know how long it will be here, but it was extended a little longer. If you can go on the week days the crowds are way smaller.
You are better off for reservations as only a limited number of people are allowed. The basic plus tickets all ow a two hour flexibility so you don't have to be on time. However, you may still wait during the busy times.
The only eat to get in is to purchase your advanced ticket.
Yes, you need to reserve your ticket and time slot. I believe the exhibit runs into 2022.
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