It says on their website that tickets expire after 2 weeks. That said, there is no advantage to buying tickets in advance. It's the same price at the door, and you still need to wait the same line and there's the potential for you to lose your money if your trip doesn't work out when originally planned
If the ticket is purchased with your name, I think you should be good. But it's better to call them to check if they is the case.
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