How does the line/wait work exactly? Do you stand in line to buy a ticket, then stand in a seperate line and wait to enter? Or do they give you a time slot after you purchase the ticket allowing me to wait in my car?

Theres only one line. Tours are every 15 minutes with a average of 13 people per group. So the line moves fairly quick. While waiting in line they group you then you go to purchase the ticket and then the tour starts right after. Basically, you pay right before the tour starts. There's no waiting after you got your tickets.

Buy tickets in advance online but you wait in line to get in. So just wait in line, once a group gets inside, you buy ticket right before you start the tour.

Easier to buy tickets online before hand. Dont worry about the heat. When standing in line, they have a mist system set up. Best money I spent in Vegas!!

You can book online but you queue the same as everyone else. There's no set times for entering. I'd just get there early and be one of the first, that's what we did.