You can make reservations online, it will tell you their open slots. Depending what time of year you plan to go, I recommend you make reservations ahead of time as it gets booked.
The day before or as soon as you can
I booked only 4 days out and didn't have a problem. But if you have a group bigger than 4 I would recommend a little further out.
I was able to book my tickets the day before I went there.
I guess u should do it a month in advance because they are pretty busy. If I were u, I would do it now
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